2. Multiple Endocrine Neoplasia Type 2

Transcription

1 2. Multiple Endocrine Neoplasia Type 2 Mimi I. Hu, MD Robert F. Gagel, MD Introduction Multiple endocrine neoplasia type 2 (MEN-2) is a rare, autosomal dominant inherited syndrome characterized by medullary thyroid carcinoma (MTC) and pheochromocytoma ( Table 2-1 ). The subtypes of MEN-2A and MEN-2B are distinguished by the additional association with parathyroid hyperplasia in MEN-2A (Sipple syndrome) and mucosal ganglioneuromas in MEN-2B. MEN-2B patients typically have a marfanoid habitus (long arms and legs with thin fingers) and thick corneal nerves. Familial MTC (FMTC) is recognized as a variant of MEN-2A defined by the presence of MTC or C-cell hyperplasia in multiple family members, without parathyroid hyperplasia or pheochromocytomas. MEN-2 is estimated to affect 1 out of every to people. MEN-2A is more common than FMTC, while MEN-2B is the least common hereditary syndrome of the three. MTC represents 4% of all new cases of thyroid cancer in a given year in the United States. Of the new cases, 70% to 75% are sporadic, and 25% are hereditary ( 1 ). This article describes the MEN-2 syndromes with an emphasis on the pathogenesis and management of MTC, the most prevalent malignancy associated with MEN-2 syndromes. Pheochromocytomas are discussed in another article. This article emphasizes how the genotype-phenotype correlation seen with hereditary MTC makes it an ideal disorder for the incorporation of basic science with patient management. Prophylactic thyroidectomy recommended for carriers of the disease-activating genetic mutation is recognized as the most effective primary prevention of MTC. Additionally, understanding the pathogenesis of MTC has led to the investigation of tyrosine kinase inhibitors (TKIs) and other targeted therapies for management of progressive, metastatic MTC. Clinical cases from the authors practice are included to highlight the complexities in the management of MEN-2 patients. Translational Endocrinology & Metabolism, Volume 2, Number 4,

2 TABLE 2-1. Summary of MEN-2 Syndromes MEN-2A MEN-2B Tumors MTC (>90%) MTC (100%) Pheochromocytoma (0%-50%) Pheochromocytoma (50%) Parathyroid hyperplasia (0%-20%) Ganglioneuromas of mucosa and gastrointestinal tract (>90%) Clinical features Cutaneous lichen amyloidosis Marfanoid habitus RET gene mutations Hirschspung disease Parathyroid hyperplasia: hypercalcemia, nephrocalcinosis, polyuria, constipation, abdominal pain MTC: neck mass, diarrhea, flushing Thick corneal nerves Inability to make tears Thickened lips Constipation, feeding problems, or megacolon in infancy Pheochromocytoma: tachycardia, palpitations, anxiety, headaches, hypertension Codon 634 (most common); associated with cutaneous lichen amloidosis Codons 609, 611, 618, 620; associated with Hirschsprung disease Codon 918 (most common) Abbreviations: MEN-2, multiple endocrine neoplasia type 2; MTC, medullary thyroid carcinoma; RET, rearranged during transfection. Clinical Presentation MEN-2A is characterized by MTC in more than 90% of gene carriers, unilateral or bilateral pheochromocytomas in 50% of carriers, and parathyroid hyperplasia in approximately 20% of carriers. Unlike that which is seen with MEN-1, the hyperparathyroidism associated with MEN-2A rarely occurs early in life, with a reported median age of diagnosis of 38 years ( 2 ). MEN-2A with Hirschsprung disease is an uncommon variant where children present in childhood with megacolon or obstructive symptoms. MEN-2A with cutaneous lichen amyloidosis has been reported, where patients exhibit a pruritic, cutaneous form of amyloid located over the upper back ( 3 ). Most commonly, the skin abnormality develops in the second or third decade of life; however, in some reported examples, localized pruritus has been noted during childhood. 46 Translational Endocrinology & Metabolism: Neoplasia Update

3 In MEN-2B patients, MTC occurs 100% of the time; pheochromocytomas arise in 50% of patients, and mucosal neuromas localized on the distal tongue, lips, eyelids, and the gastrointestinal tract are found in more than 90% of the patients. C-cell hyperplasia and MTC associated with MEN-2B generally develop much earlier and generally have a more aggressive course than in those with MEN-2A; metastatic MTC has been described during the first year of life in MEN-2B patients. MEN-2 patients may come to clinical attention due to symptoms suggestive of underlying MTC: presence of a neck mass, diarrhea (thought to be caused by tumoral production of a humoral factor), flushing, or rarely Cushingoid features (due to ectopic tumoral production of adrenocorticotropic hormone). An underlying pheochromocytoma associated with MEN-2 is suspected when a patient exhibits symptoms of excessive beta-adrenergic activity from overproduction of epinephrine: tachycardia, palpitations, anxiety-like complaints, and intermittent headaches ( 4 ). Hypertension is less striking, unless there exists a large tumor. Occasionally, patients may have no symptoms of an underlying pheochromocytoma, but plasma metanephrines will be elevated. Primary hyperparathyroidism (PHPT) may present with hypercalcemia, renal stones, polyuria, constipation, or abdominal pain. Finally, patients may present for initial evaluation and screening due to a family history suggestive of MEN syndrome or a rearranged during transfection ( RET ) proto-oncogene mutation has been identified in a family member. Etiology Hazard et al first described the pathologic findings in MTC in 1959, and Williams identified MTC as arising from the parafollicular C-cells of the thyroid in 1966 ( 5 7 ). Transformation of C-cells in hereditary MTC syndromes follows a series of histologic stages: normal, C-cell hyperplasia, microscopic MTC, and finally macroscopic carcinoma. Calcitonin overproduction with MTC was recognized later, leading to its use as a marker for biochemical diagnosis and disease progression in MTC ( 8, 9 ), and it was subsequently learned that carcinoembryonic antigen (CEA) is also produced by this tumor ( 10 ). In 1961, Sipple described the association between MTC and pheochromocytoma, which is now recognized as part of the MEN-2 syndromes ( 11 ). MEN-2A was first linked to a genetic defect on chromosome 10 in 1987 ( 12 ). In 1993, activating germline point mutations of the RET protooncogene were found to be responsible for the MEN-2A and FMTC syndromes ( 13, 14 ). Eventually, in 1994, RET mutations were linked to Multiple Endocrine Neoplasia Type 2 47

4 MEN-2B. These mutations led to the expression of an abnormally active RET transmembrane tyrosine kinase receptor, which mediates cell proliferation, differentiation, survival, and migration. More than 95% of MEN-2 families have germline RET mutations, with codon C634R (cysteine to arginine) being the most common mutation in MEN-2A, and M918T (methionine to threonine) the most common in MEN-2B. Forty percent of sporadic MTC cases are associated with somatic RET mutations, typically in codon 918, which conveys a similarly high level of aggressiveness as that seen with tumors with germline codon 918 mutations ( ). The RET Proto-oncogene and RET Receptor The RET proto-oncogene encodes a receptor belonging to the family of tyrosine kinase receptors. RET is expressed by neural crest derived cell lineages (ie, thyroid C cells, adrenal medullary cells, parathyroid cells, parasympathetic and sympathetic and colonic ganglia cells, urogenital tract cells, and others). RET normally regulates cell proliferation, migration, differentiation, and survival during embryogenesis. RET knockout mice have defective renal development and fewer thyroid C-cells and lack enteric innervation ( 18 ). Humans lacking RET expression due to inactivating germline mutations develop Hirschsprung disease ( 19 ). Unregulated RET activation leads to various cancers, including hereditary MTC ( 20 ). The RET gene, located on chromosome 10q11.2, consists of 21 exons with 55,000 base pairs ( 21, 22 ). RET encodes a 1-pass transmembrane receptor with a large extracellular portion containing 4 calcium-dependent cell adhesion (cadherin) domains that mediate the conformational properties needed to interact with ligands and coreceptors ( 23 ). Additionally, the extracellular portion of the receptor contains multiple glycosylation sites and a cysteine-rich region necessary for the tertiary structure of the protein and receptor dimerization. The intracellular domain of RET contains 2 tyrosine kinase regions that activate intracellular signal transduction pathways. Three isoforms of RET are produced by alternative splicing: RET9 (short isoform), RET43 (intermediate isoform), and RET51 (long isoform), which differ by 9, 43, and 51 amino acids at the C terminus, respectively. Each isoform has a different role in the development of kidney and neural crest derived cells ( 24 ). RET activation requires the association of a ligand [glial cell line derived neurotrophic factor (GDNF) or related molecules, including neurturin ( 25 ), artemin ( 26 ), or persephin ( 27 )], to a membrane surface coreceptor, glycosylphosphatidylinositol-anchored GDNF-family alpha (GFR α ) ( 28 ). Four 48 Translational Endocrinology & Metabolism: Neoplasia Update

5 subtypes of coreceptors have been identified (GFR α 1-4). The GDNF-GFR α complex interacts with the RET receptor to permit its dimerization with another RET receptor. This triggers autophosphorylation of tyrosine residues on the intracellular domains of RET ( 22, 29 ). The activated tyrosine residues serve as docking sites for adaptor proteins, which coordinate intracellular signal transduction pathways that are described later in this article. Genotype-Phenotype Correlation Since the initial discovery of RET mutations associated with MEN-2 syndromes, there has been recognition and increased identification of phenotypes associated with specific activating mutations of RET. Table 2-2 shows an overview of the current understanding of RET mutations and presents the clinical syndromes associated with different mutations of RET. The specific germline RET mutation can be predictive of the clinical presentation of tumor development (MTC, pheochromocytomas, parathyroid hyperplasia) and of the aggressiveness of MTC disease course ( 28 ). This may be related to variable phosphorylation of docking sites of mutated RET receptor observed in different syndromes, which in turn leads to initiation of different intracellular signaling pathways ( 30, 31 ). MEN-2A are caused by mutations in the extracellular cysteine-rich regions of RET in exons 10 and 11. These mutations lead to constitutive dimerization without GDNF ligand association and, consequently, activation of RET receptors ( 32 ). The MEN-2A mutations have primarily involved missense mutations substituting cysteine for another amino acid in codons 609, 611, 618, 620, 630, and 634. Codon 634 mutations are the most common; they are found in 85% of patients with MEN-2A and account for 80% of all cases of MEN-2 syndrome ( 33 ). Cutaneous lichen amyloidosis has been most often described in families with codon 634 mutations and in 1 kindred with a codon 804 mutation ( 3, 34 ). Hirschsprung disease is associated with mutations of exon 10, most often with codon 620, as well as with codons 609, 611, and 618 ( 35, 36 ). MEN-2B involves mutations of the intracellular tyrosine kinase domains of RET (in exons 13-16), which activate RET enzymatic function without the need for receptor dimerization ( 28 ). Of patients with MEN-2B, 95% have a germline M918T mutation, and <4% have an A883F mutation ( 16, 17, 37, 38 ). M918T has been shown to alter the substrate-binding pocket of RET, which changes its specificity for an adaptor protein that mediates further intracellular signaling pathways ( 39 ). In addition, Gujral et al have reported that the M918T mutation confers a 10-fold increase in Multiple Endocrine Neoplasia Type 2 49

6 TABLE 2-2. Genotype-Phenotype Correlation with Hereditary MTC Syndromes ( 1, 109, 110 ) Exon Codon MTC +PHEO +PHPT +CLA +HSCR MEN-2B ATA Risk 10 C609R/G/F/ S/Y C611R/G/F/ S/W/Y C618R/G/F/ S/Y C620R/G/F/ S/W/Y B B B B 11 C630R/F/S/Y B C634R/G/F/ S/W/Y + + C 13 E768D A L790F + + A Y791F + + A 14 V804M/L A 15 A883F D S891A + + A 16 M918T D Abbreviations: ATA, American Thyroid Association CLA, cutaneous lichen amyloidosis; HSCR, Hirschsprung s disease; MEN, multiple endocrine neoplasia; MTC, medullary thyroid carcinoma; PHEO, pheochromocytoma; PHPT, primary hyperparathyroidism. adenosine triphosphate (ATP) binding affinity of the catalytic site of RET and greater stability of the receptor-atp complex, thereby increasing RET tyrosine kinase activity ( 38 ). Novel tandem mutations of valine 804 (V804M) and glutamate 805 (E805K) have been described in a patient with MEN-2B, causing an alteration of the hinging motion of the tyrosine kinase, and, in turn, increasing kinase activity ( 40 ). MEN-2B codon mutations, most notably codon 918, are associated with most aggressive form of MTC. FMTC patients exhibit germline mutations that are equally distributed throughout the extracellular and intracellular portions of RET. Mutant RET proteins associated with FMTC, considered the least aggressive of the hereditary MTC syndromes, demonstrate less kinase and oncogenic activities than MEN-2A RET proteins ( 32 ). The information collected since 1993 on RET mutations and correlative clinical expression has led to consensus on using genetic information to 50 Translational Endocrinology & Metabolism: Neoplasia Update

7 provide management recommendations for prevention of morbidity and mortality associated with hereditary MTC ( 1, 41 ). The relative aggressiveness of MTC has been determined by noting the earliest age at which MTC has been diagnosed or associated with lymph node metastases with a specific mutation. Based on genotype-phenotype correlation found in carriers of RET mutations, a risk stratification system was developed by the Seventh International Workshop on MEN based on the aggressiveness of MTC with known RET mutations, described in the 2009 American Thyroid Association (ATA) guidelines for MTC management ( 1 ). ATA level D mutations (codons 883 and 918) are associated with the highest risk for MTC, developing metastases and having the youngest age of onset. ATA level C mutations (codon 634) have a high risk for aggressive MTC. ATA level B mutations (codons 609, 611, 618, 620, and 630) impart a lower risk for aggressive MTC. ATA level A mutations convey the least high risk. However, it is well-recognized that although this risk level stratification has been established, there can be variability in the expression of MEN-2A and MTC behavior between RET mutations within the same ATA risk level and even within kindreds with the same mutation. Further investigation of the intracellular signaling pathways associated with RET mutations may reveal the cause of such variability. Intracellular Signaling Pathways Activated RET kinase receptor leads to stimulation of various important intracellular signaling proteins and pathways that mediate cell growth, differentiation, and invasiveness: Src ( 42 ), phosphatidylinositol 3-kinase- AKT (PI3K/AKT) ( ), and mitogen-activated protein kinase (MAPK) ( 45 ). Src has been found to mediate the signaling between RET and focal adhesion kinase (FAK), which regulates cell growth and migration and supports the metastatic potential of cancer cells ( 46, 47 ). Although PI3K/AKT activation has been found in both MEN-2A and MEN-2B, greater activity has been demonstrated in MEN-2B ( 43 ). PI3K/AKT activates downstream signals, such as mammalian target of rapamycin (mtor) and nuclear factor κ B (NF- κ B). NF- κ B prevents cell apoptosis, and inhibiting this may lead to tumoral cell death in MTC ( 48, 49 ). The well-described MAPK pathway involves an activated tyrosine kinase receptor (such as RET/PTC [papillary thyroid carninoma] receptor in papillary thyroid carcinoma) stimulating Ras to bind to RAF kinases (primarily BRAF in thyroid follicular cells). BRAF then activates mitogen-activated protein kinase/extracellular-signal-regulated kinase, which consequently activates ERK (extracellular-regulated kinase), a kinase that regulates nuclear transcription factors necessary for cell Multiple Endocrine Neoplasia Type 2 51

8 differentiation, proliferation and survival ( 50 ). RET has been found to directly phosphorylate and activate ERK ( 51 ). Other Kinase Receptor Mediators of Pathogenesis Angiogenesis is recognized as a critical process in facilitating tumor cell growth and invasiveness by supplying nutrients and oxygen and providing a way to spread distantly and develop metastases ( 52 ). Interaction of vascular endothelial growth factor (VEGF), most prominently VEGF-A type, with VEGF-receptor (VEGFR)-2, mediates angiogenesis and cell proliferation and survival via increased MAPK and PI3K/AKT signaling ( 53 ). VEGF binds to VEGFR-1 with greater affinity than to VEGFR-2, but leads to weaker signal transduction than that observed with the VEGF/VEGFR-2 complex. VEGF-A, VEGFR-1, and VEGFR-2 are overexpressed in MTC tumor tissue ( 54, 55 ). Recent investigations have highlighted the importance of other receptor mediators of tumorigenesis besides VEGFR. The epidermal growth factor receptor (EGFR) is overexpressed in several types of tumors, including in metastatic MTC tumors compared with primary tumors ( 56 ). EGFR has been shown to stimulate RET phosphorylation and activation, and inhibition of EGFR leads to diminished cell growth ( 57 ). The receptor product of MET oncogene, c-met, has been detected in MTC; however, its relevance to MTC invasiveness or survival has not been clarified ( 58, 59 ). Fibroblast growth factors (FGFs) have been recognized as mediators of cell growth, angiogenesis, and resistance to antiangiogenic therapies ( 60 ). MTC cells express FGF-receptor 4 (FGFR4), and inhibition of FGFR4 phosphorylation led to decreased MTC cell growth ( 61 ). Diagnostic Procedures for MEN-2 Once the presence of a hereditary syndrome is suspected, genetic testing for MEN-2 is extremely valuable. The primary goal is to identify and treat the several manifestations of MEN-2 before they become life threatening. Life-threatening manifestations include metastases from MTC and sudden death associated with pheochromocytoma. An understanding of the ATA risk level associated with a specific codon mutation is important in counseling patients and family members of timing of prophylactic thyroidectomy, parathyroidecomy and/or screening for pheochromocytoma. An additional goal with genetic evaluation is to provide essential information for the counseling of family members about the potential for transmission to the next generation. 52 Translational Endocrinology & Metabolism: Neoplasia Update

9 The decision to have genetic testing is a personal one and should be voluntary after appropriate genetic counseling. Genetic counseling to individuals before obtaining the genetic test involves the elaboration of the process of genetic testing, the fundamentals of autosomal-dominant inheritance in MEN-2, and clinical features of the syndrome and the implication for family members. The ATA guidelines for MTC recommend that all patients with a personal history of primary C-cell hyperplasia, MTC, or MEN-2 or with a family history of MEN-2 or FMTC should be offered germline RET testing ( 1 ). Licensed genetic counselors can be found via the National Society of Genetic Counselors Web site ( www. nsgc.org ) or the National Institutes of Health Web site ( search/genetics_services ). Laboratory testing should be directed toward identifying possible underlying tumors: parathyroid hyperplasia (calcium, phosphorus, albumin, intact parathyroid hormone), medullary thyroid carcinoma (calcitonin, CEA, thyroid stimulating hormone), and pheochromocytoma (plasma free metanephrines/normetanephrines or 24-hour urinary metanephrines/ normetanephrines). Screening for PHPT prior to a planned thyroidectomy is necessary when MEN-2A is suspected or identified, as it is recommended to surgically manage the hyperparathyroidism concomitantly. An underlying pheochromocytoma must be excluded prior to thyroidectomy with one of the following: laboratory testing as previously mentioned, negative RET mutational status and family history, or negative adrenal computed tomography or magnetic resonance imaging ( 1 ). If an underlying pheochromocytoma is present, it should be surgically resected after appropriate preoperative preparation and prior to surgery for MTC or PHPT. Prior to surgery for clinically apparent MTC, ultrasound of the neck to include the superior mediastinum, central compartment, and bilateral lateral neck compartments should be done. Treatment of Medullary Thyroid Carcinoma Prophylactic Surgical Management of Preclinical Hereditary MTC Cure rates are low when MEN-2 patients have palpable MTC lesions. Consequently, surgical resection based on RET mutation prior to the development of clinically detectable disease (ie, normal thyroid on physical examination, no suspicious lymph nodes or thyroid nodules >5 mm on ultrasound) offers the best chance for prevention of disease or metastases. Multiple Endocrine Neoplasia Type 2 53

10 In addition to offering best chance for cure with intervention prior to development of metastases, this approach would avoid a central compartment lymph node dissection, which increases the risk for hypoparathyroidism and recurrent laryngeal nerve injury ( 1 ). The 2009 ATA guidelines recommend total thyroidectomy for patients with an ATA level D risk mutation (codon 918) before 1 year of age at an experienced tertiary care setting ( Figure 2-1 ). ATA level C risk mutation (codon 634) should undergo surgery before age 5 years. Carriers of ATA level B risk mutations should be considered for surgery before age 5 years, but surgery may be delayed if there is a less aggressive family history of MTC, no concerning features on ultrasound, and normal calcitonin. Carriers of ATA level A mutations may be considered for surgery beyond 5 years of age if similar stringent criteria are met. Treatment of Clinically Apparent MTC Surgical resection consisting of total thyroidectomy and central compartment (level 6) lymph node dissection remains the most definitive curative modality available for clinically apparent MTC, with the adequacy of the ATA Risk Level Risk Levels A, B, or C Risk Level D Testing: - RET test: < 3-5 years old - 1 st Calcitonin: > 3-5 years old - 1 st Ultrasound: > 3-5 years old Prophylactic Thyroidectomy: - Risk A: May delay beyond 5 years old if stringent criteria are met.* - Risk B: Consider before 5 years old, or delay beyond 5 years old if stringent criteria are met.* - Risk C: Before 5 years old Testing: - RET test: ASAP and 1 year old - 1 st Calcitonin: 6 months old, if surgery not done yet - 1 st Ultrasound: ASAP and 1 year old Prophylactic Thyroidectomy: - ASAP and 1 year old FIG 2-1. Recommendations for testing and prophylactic thyroidectomy based on American Thyroid Association (ATA) risk level. *Normal annual basal ± stimulated serum calcitonin, normal annual neck ultrasound, less aggressive medullary thyroid carcinoma family history, and family preference ( 1 ). Abbreviations: ASAP, as soon as possible; RET, rearranged during transfection. 54 Translational Endocrinology & Metabolism: Neoplasia Update

11 initial operation being the most important determinant of outcome ( 1 ). A review of a prospective database of patients with MTC, who received total thyroidectomy with compartment-oriented surgery, revealed that only 13% of patients with invasive MTC had recurrence of disease ( 62 ). Biochemical cure of MTC varies depending upon the extent of lymph node involvement at the time of surgery (75% to 90% in patients without lymph node involvement but 20% to 30% in those with lymph node involvement) ( 63 ). Due to the high chance of persistent disease in patients with lymph node metastases or large primary tumors, prophylactic lateral neck dissection is not recommended, especially given the potential complications from extensive neck dissection. Thus, the 2009 ATA guidelines recommend performing lateral neck dissection for patients with demonstrable disease on preoperative imaging in the setting of no distant metastases or limited distant metastases ( 1 ). Surgical goals in the setting of extensive distant metastases or advanced local disease are palliative. Distant metastatic disease represents a therapeutic challenge, as there are no curative options available at this time. Radiation therapy and chemotherapy regimens for MTC historically have been nonspecific and primarily palliative in nature. However, within the last decade, there has been remarkable growth in the development of pharmacologic agents directed at progressive, metastatic MTC. Pharmacologic Agents for the Treatment of Medullary Thyroid Carcinoma Doxorubicin used as a single agent halted disease progression in 3 patients in 1 reported study ( 64 ). In a phase 2 study where 10 patients with MTC were treated with a combination of doxorubicin, cisplatin, and vindesine, only 1 patient achieved a partial remission, and 3 patients had progression of disease ( 65 ). Another study evaluated alternating a combination of fluorouracil (5-FU) streptozocin with a 5-FU dacarbazine combination in 20 patients with metastatic MTC. Eleven patients had stabilization of their disease, and 3 achieved partial responses ( 66 ). Overall, combinations of chemotherapeutic agents have demonstrated partial responses in about 20% of patients with MTC, offset by the significant side effects associated with cytotoxic chemotherapy ( 63 ). Other therapeutic agents used in MTC, reported in small case studies or trials, include interferon-alpha ( 67 ), high-dose radioimmunotherapy with 131 I-MN-14 F(ab)2 anti-carcinoembryonic antigen monoclonal antibody followed by autologous hematopoietic stem cell rescue ( 68 ), calcitoninpulsed dendritic cells ( 69 ), and somatostatin analogues (octreotide and Multiple Endocrine Neoplasia Type 2 55

12 lanreotide) ( ). These agents produced various responses in tumor progression and symptomatology but overall were not likely to offer clinical benefit. Thus, they are not recommended for management of progressive MTC at this time. Due to the clinical success of TKIs in the treatment of other cancers, RET receptor and other mediators of tumorigenesis in MTC have become important potential therapeutic targets. Pharmacologic agents inhibiting RET autophosphorylation and activation of intracellular signaling pathways have shown the most clinical promise. A TKI is a small molecule that competes with the ATP binding site of the catalytic domain of a tyrosine kinase. The occupation of this site inhibits the autophosphorylation and activation of the receptor and prevents further activation of intracellular signaling pathways. A TKI can be specific to 1 or many homologous tyrosine kinases ( 73 ). A TKI selective for RET only is currently not available for clinical use, but many other TKIs are being evaluated in the treatment of MTC ( Table 2-3 ). As a result of the intense clinical investigation of various agents within the last decade, vandetanib was the first pharmacologic agent to be approved by the US Food and Drug Administration (FDA) in April 2011 for the treatment of symptomatic or progressive MTC in patients with unresectable, locally advanced, or metastatic disease. Imatinib Mesylate Imatinib mesylate (Gleevec, Novartis Pharmaceuticals, East Hanover, New Jersey) exemplifies the effectiveness of selective tyrosine kinase inhibition in the treatment of chronic myelogenous leukemia, gastrointestinal stromal tumors, and dermatofibrosarcoma protuberans. Imatinib mesylate specifically targets constitutively active BCR-ABL (breakpoint cluster region-abl tyrosine kinase), platelet-derived growth factor receptor (PDGFR), and c-kit. Owing to the similarity of RET with c-kit, imatinib mesylate has been studied in cell lines expressing several types of mutant RET (codons 634 and 918). One study showed a dose-dependent decrease in proliferation of TT (C634-RET cell line) cells after exposure to 3 different TKIs (imatinib mesylate, genistein, or allyl geldanamycin). This observation has been attributed to disruption of the tyrosine kinase activity of the RET receptor and enhancement of RET degradation ( 74 ). Unfortunately, the concentration of imatinib mesylate needed to inhibit 50% of cell growth (IC 50 ) in vitro is approximately 25 µm, requiring therapeutic doses that would be intolerable in humans ( 75 ). Nonetheless, an openlabel, non-randomized phase 2 dose-escalating trial was conducted to evaluate the use of imatinib mesylate for endocrine tumors expressing 56 Translational Endocrinology & Metabolism: Neoplasia Update

13 TABLE 2-3. Tyrosine Kinase Inhibitors in Clinical Studies for Medullary Thyroid Carcinoma Drug Relevant Targets Phase of Study Progression Before Enrollment n PR (%) SD >6 Months (%) Median PFS Motesanib VEGFR2 2 Yes ( 80 ) RET PDGFR Kit Sorafenib VEGFR2 2 No ( 83 ) RET RET/PTC3 RAF PDGFR c-kit Sunitinib VEGFR2 2 Yes NA ( 88 ) RET RET/PTC3 PDGFR 2 Yes ( 89 ) FLT-3 Cabozantinib VEGFR2 1 No NA ( 91 ) RET c-met c-kit FLT-3 Vandetanib VEGFR2 2 No ( 95 ) RET 3 No NA NR ( 96 ) RET/PTC3 2 * No NA ( 94 ) EGFR Reference *Study with vandetanib 100 mg/d. Abbreviations: EGFR, epidermal growth factor receptor; FLT-3, fms-like tyrosine kinase-3; NA, not applicable NR, not researched; PDGFR, platelet-derived growth factor receptor; PFS, progression-free survival; PR, partial response; PTC3, a fusion protein made by the fusion RET/PTC3 gene so PTC3 is papillary throid cancer 3; RET, rearranged during transfection; VEGFR2, vascular endothelial growth factor-2. c-kit and/or PDGFR (MTC, n=6). In that trial, disease progressed in 4 of the MTC patients, and the other 2 patients discontinued treatment because of adverse events (AEs). Additionally, since no objective response was Multiple Endocrine Neoplasia Type 2 57

14 demonstrated in any of the other tumors treated with imatinib mesylate and since significant toxicity (eg,, bleeding, fatigue, anorexia, nausea) occurred, the investigators concluded that monotherapy with imatinib mesylate did not demonstrate clinical utility in the treatment of malignant endocrine tumors ( 76 ). A phase 2 trial using imatinib mesylate (600 mg/d) in 15 patients with metastatic MTC, led to no objective responses, while 4 patients had stable disease for over 24 months. Toxicity was noted to be considerable ( 77 ). Motesanib Motesanib (AMG706, Amgen Inc, Thousand Oaks, California) is a multikinase inhibitor targeting VEGFR1-3, RET, PDGFR, and Kit receptors with antiangiogenic and direct antitumor activity. A phase 1 study of motesanib in patients with advanced solid tumors included a subset of thyroid cancer patients ( 78 ). The histologic subtypes of thyroid carcinoma represented were papillary (n=2), follicular (n=2), Hurthle cell (n=1), anaplastic (n=1), and medullary (n=1). Partial objective responses (ie, >30% reduction in tumor diameter) according to Response Evaluation Criteria in Solid Tumors (RECIST) were seen in 3 patients (medullary, papillary, and follicular subtypes). AEs included diarrhea, hypertension, fatigue, dizziness, nausea, and headache, which are typical of this class of drugs. A large, multicenter, open-label phase 2 trial evaluating motesanib in patients with progressive differentiated thyroid carcinoma (DTC) and progressive or symptomatic MTC was conducted ( 79, 80 ). Of the 91 patients with MTC, 2% had partial responses, while 47% had stable disease for at least 24 weeks. The MTC cohort exhibited a lower response rate than the 14% partial response rate seen in the DTC cohort. This may be attributable to the finding that the plasma concentrations (peak and trough) of motesanib were lower in MTC patients than with the DTC cohort. Further clinical investigations with this agent are not being pursued at this time for MTC. Sorafenib Sorafenib (Nexavar, BAY , Bayer Pharmaceuticals Corp, West Haven, Connecticut) is a biaryl urea compound developed to inhibit BRAF kinase but which has subsequently been found to inhibit the activity of tyrosine kinases as well (RET, VEGFR-2, VEGFR-3, PDGFR- β, c-kit, and fms-like tyrosine kinase-3 [FLT-3]). Sorafenib is approved by the FDA for the treatment of advanced renal cell carcinoma and unresectable hepatocellular carcinoma. Carlomagno et al reported that BAY 58 Translational Endocrinology & Metabolism: Neoplasia Update

15 was able to inhibit RET function and oncogenic activity in vitro in RET/PTC1 and TT carcinoma cell lines ( 81, 82 ). Their results showed inhibition of RET activity and decreased growth progression, even in cells carrying the RET V804L mutation, which has conferred inherent resistance to other TKIs. A single-institution phase 2 clinical trial of BAY in patients with metastatic, locally advanced, or recurrent MTC had 2 groups: hereditary MTC and sporadic MTC ( 83 ). Progression prior to study enrollment was not required in this trial. The hereditary MTC arm was terminated early due to slow accrual. Of the 16 patients enrolled in the sporadic MTC arm, 1 had partial response (PR, 6.3%); 14 had stable disease (SD, 87.5%), and 1 was not evaluable but did demonstrate progression clinically. Median progression-free survival (PFS) was 17.9 months. The post hoc analysis of the patients who had progression prior to study entry (n=10) showed PR 10%, SD 40% of 15 months, and SD 40% of 6 months. Common AEs were diarrhea, hand-foot-skin syndrome, rash, and hypertension. Less commonly, sorafenib has been associated with actinic keratoses or keratoacanthoma-type squamous cell carcinomas (KA-SCC); thus, use of such targeted therapies should be limited to physicians familiar with the potential AEs and their management ( 84, 85 ). Fortunately, KA-SCC has not been reported to metastasize, and spontaneous regression has been reported ( 84 ). Although sorafenib is not approved for thyroid carcinomas, the recently updated National Comprehensive Cancer Network (NCCN) guidelines consider the use of sorafenib for advanced, progressive MTC if clinical trials or vandetanib are not available or appropriate ( 86 ). Sunitinib Sunitinib (Sutent, SU11248, Pfizer, Inc, New York, New York) inhibits VEGFR1-3, RET, RET/PTC, PDGFR, and FLT-3 ( 87 ). SU11248 is approved in the United States and Europe for use in renal cell carcinoma and gastrointestinal stromal tumors. A French phase 2 clinical trial evaluating sunitinib in unresectable differentiated thyroid carcinoma (n=12) and progressive MTC (n=15) ( 88 ). The interim analysis of the patients with MTC reported PR of 33% and SD (>6 months) of 27%; median PFS data were not available. Another phase 2 multicenter, open-label study presented at the annual meeting of the American Society of Clinical Oncology in 2010 reported the results of sunitinib given to MTC patients who had progression within 6 months of study enrollment (n=25) ( 89 ). PR of 35% (median duration of response 37 weeks) and SD of 57% (median duration of response 32 weeks) were described. In the patients in whom a germline Multiple Endocrine Neoplasia Type 2 59

16 or somatic RET mutation was found in tumor tissue, the 1-year probability of PFS was 88% (95% confidence interval [CI], 43% to 98%); notably, clinical benefit (PR+SD) was observed in 7 of 9 MTC patients with an M918T mutation of >24 weeks. Common or severe AEs the sunitinib studies, it may have Based on the recent report of include fatigue, diarrhea, palmar-plantar greater efficacy in patients with erythrodysesthesia, neutropenia, and hypertension. As is the case with sorafenib, suni- MTC than sorafenib. tinib can be considered for advanced, progressive MTC if clinical trials and/or vandetanib are not available or appropriate ( 86 ). Based on the recent report of the sunitinib studies, it may have greater efficacy in patients with MTC than sorafenib. Lenvatinib Lenvatinib (E7080, Eisai, Woodcliff Lake, New Jersey) is a TKI targeting VEGFR1-3, FGFR1-4, RET, c-kit, and PDGFR- β. Combined inhibition of RET and FGFR4 has been shown to slow MTC cell growth ( 61 ). There is an ongoing phase 2 study of patients with progressive MTC and DTC in 2 separate cohorts. Cabozantinib Cabozantinib (XL184, Exelixis, Inc, San Francisco, California) is a TKI of VEGFR1, -2, c-met, RET, c-kit, and FLT-3 ( 90 ). The additional target of c-met, which binds to hepatocyte growth factor for activation, may convey synergistic activity against growth of MTC cells ( 58 ). A phase 1 study of cabozantinib in advance solid tumors was enriched for patients with MTC as clinical benefit was noted ( 91 ). Thirty-seven of the 85 patients enrolled in this trial had MTC, confirmed PR of 29%, and clinical benefit of 6 months (PR + SD) 68% were reported for the MTC cohort. The maximally tolerated dose was 175 mg with dose-limiting AEs due to palmar plantar erythrodysesthesia, mucositis, and elevations of aspartate aminotransferase, alanine aminotransferase, and lipase. These findings led to the development of a phase 3 randomized, placebo-controlled, multicenter trial evaluating patients with progressive MTC within 14 months of study enrollment; this study recently met full enrollment in early The primary objective is to evaluate PFS; a secondary objective is to evaluate overall survival precluding crossover if progression occurs while on placebo. This agent may have beneficial effects on bone metastases, as Gordon et al presented data on the efficacy and safety of cabozantinib 60 Translational Endocrinology & Metabolism: Neoplasia Update

17 in 9 tumor types, which did not include MTC ( 92 ). Fifty-nine out of 68 patients with castration-resistant prostate cancer, breast cancer, and melanoma with bone metastases demonstrated partial or complete resolution of bone lesions by bone scan imaging. Plasma C-telopeptide, a marker of osteoclastic activity, declined 50% from baseline across all tumor types in 55% of patients. The phase 3 trial in MTC patients has a subgroup of patients with bone-only disease (ie, nonmeasurable disease by RECIST). As metastatic bone disease in MTC is often difficult to treat and has been poorly responsive to other treatments, an agent that can target bone as well as soft tissue disease is much needed. Vandetanib Vandetanib (Caprelsa, ZD6474, AstraZeneca Pharmaceuticals LP, Wilmington, Delaware) is a selective inhibitor of RET, VEGFR-2 and -3, and, to a lesser extent, EGFR. ZD6474 inhibits RET enzymatic activity (IC nm) in vivo by blocking phosphorylation and signaling of RET/PTC3 As metastatic bone disease in and RET/MEN-2B oncoproteins and of the MTC is often difficult to treat EGFR/RET chimeric receptor; in vitro it and has been poorly inhibited formation of tumors after injecting NIH-RET/PTC3 cells into nude mice an agent that can target bone responsive to other treatments, ( 93 ). Two phase 2 trials evaluated the use as well as soft tissue disease is of ZD6474 in patients with hereditary MTC much needed. at 2 different daily dose levels: 100 mg ( 94 ) and 300 mg ( 95 ). The open-label trial of vandetanib (300 mg/d) enrolled 30 patients with unresectable or metastatic hereditary MTC; patients did not need to demonstrate progression prior to enrollment. Wells et al reported that vandetanib demonstrated PR of 20% and SD of 53% in patients with a clinical benefit of 73% for 24 weeks ( 95 ). Calcitonin levels dropped by >50% for at least 4 weeks in 24 patients, and a similar magnitude of decline in CEA was seen in 16 patients. Side effects included diarrhea, rash, fatigue, nausea, hypertension, and asymptomatic QTc interval prolongation. Responses did not correlate with RET mutation. The low-dose study (100 mg) enrolled 19 patients who did not need to have progression prior to study entry; the protocol allowed for titration up to 300 mg/d when a patient demonstrated progression with the 100 mg dose, which did occur in 4 patients ( 94 ). Robinson et al reported that 16% had confirmed PR, and 53% had SD. AE profile was similar to that reported in the Wells trial ( 96 ). Asymptomatic QTc prolongation was seen in 1 patient at the 100 mg dose; there was no recurrence of this finding Multiple Endocrine Neoplasia Type 2 61

18 with adjustment of dose to 100 mg every other day. A large, multicenter, phase 3, randomized, placebo-controlled study was conducted to evaluate the effectiveness of vandetanib 300 mg/d in patients with unresectable or metastatic MTC (n=331, 231 vandetanib and 100 placebo). Nonhereditary MTC patients were included in this trial; no tumor progression prior to study entry was required. With a median follow-up of 24 months, the PFS was significantly prolonged for vandetanib vs placebo (hazard ratio [HR] 0.46, 95% CI , P <.001). Median PFS for the placebo group was 19.3 months; the median PFS for vandetanib group had not yet been reached at the time of analysis, although the predicted median was 30.5 months. Vandetanib conveyed better objective response rate (PR 45%) and disease control rate (87%) compared with placebo. There is an ongoing phase 2 trial of vandetanib at 100 mg/m 2 in pediatric patients (<18 years old) with hereditary MTC (6 of 7 patients enrolled have M918T mutation) with evidence of tumor shrinkage ( 97 ). Based on the promising results of Vandetanib was approved by the 3 studies in adults and on the fact that the FDA for symptomatic or no other effective treatment was available progressive, unresectable or for MTC, vandetanib was approved by the metastatic MTC in April FDA for symptomatic or progressive, unresectable or metastatic MTC in April Due to the risk for development of QTc prolongation, which can predispose to Torsade de pointes, lifethreatening arrhythmias, and sudden death, the agent can only be prescribed by physicians who are enrolled in the Risk Evaluation and Mitigation Strategy program ( 98 ). Prescribers must understand this serious risk and implement appropriate monitoring and management strategies: careful patient selection; obtain electrocardiograms at baseline and routinely while on treatment as recommended in the package insert; and correct electrolyte abnormalities such as hypocalcemia, hypokalemia, and hypomagnesemia. The recent NCCN guidelines have been updated to include vandetanib in its recommendations ( 86 ). Combination of Agents in Management of MTC Use of more than 1 TKI or in combination with other chemotherapeutic agents may lead to greater suppression of MTC cell proliferation and tumor invasiveness. Additionally, lower doses of TKIs may be equally effective when combined with other agents with potential minimization of AEs. Ezzat et al examined the use of imatinib mesylate alone, PD (a TKI selective for FGFR) alone, and the combination of these 2 drugs in the human MTC TT cell line and in vivo in mice with severe combined 62 Translational Endocrinology & Metabolism: Neoplasia Update

19 immu nodeficiency transplanted with MTC ( 61 ). The results showed that PD alone produced a decrease in cell proliferation and tumor growth in vivo. Additionally, the concomitant inhibition of RET and FGFR-4 autophosphorylation by the 2 drugs in combination resulted in greater suppression of tumor growth in vitro and in vivo than that produced by either drug alone. A phase 1 study of the combination of sorafenib and tipifarnib, a farnesyl transferase inhibitor that inactivates Ras and other farnesylated proteins, in patients with differentiated and medullary thyroid carcinoma refractory to other standard treatments enrolled 13 patients with MTC ( 99 ). Eight of the 13 had either a somatic or germline RET mutation. The median PFS was 15 months with PR of 38% and SD of 31%. There is ongoing phase 1/2 trial valuating the safety, tolerance, and effectiveness of vandetanib combined with bortezomib (a proteosome The recommendation to initiate inhibitor approved for multiple myeloma) targeted therapy either with in adults with MTC ( 100 ). The phase 1 data vandetanib or other agent in a showed that of the 21 patients enrolled, clinical trial setting must be 1 remains on the combination regimen, made after a clear discussion while 10 are maintained on vandetanib between the treating physician alone. Grade 3 toxicities included hypertension, fatigue, thrombocytopenia, diarrhea, for treatment and the expected and the patient on the rationale and arthralgia. No drug-related grade 4 or risks and benefits with treatment. 5 toxicities occurred. The maximally tolerated dose regimen is bortezomib 1.3 mg/m 2 intravenously on days 1, 4, 8, and 11 and vandetanib 300 mg orally daily. The phase 2 portion to compare this combination with vandetanib alone is currently enrolling. The results from these combination studies support the need for investigators to develop other trials using a combination of appropriate agents to maximize efficacy and potentially minimize toxicity. Challenges in the Medical Management of Progressive MTC Despite the exponential development of potential agents targeting oncogenic signaling pathways in MTC, there have been no reported complete response or cure in the clinical studies described previously. Additionally, survival benefit has not been proven with any of these drugs to date, although the results of the phase 3 cabozantanib study may provide insight into this issue with further analysis. Thus, the recommendation to initiate targeted therapy either with vandetanib or other agent in a clinical trial setting must be made after a clear discussion between the treating Multiple Endocrine Neoplasia Type 2 63

20 physician and the patient on the rationale for treatment and the expected risks and benefits with treatment. Patients who have long-standing indolent disease, although widely metastatic, may not have increased survival benefit and could sustain unacceptable side effects with targeted therapies (see Case 2-1). Additionally, the likely toxicities of TKIs may be less life threatening than those experienced with cytotoxic agents; however, AEs are common and expected and can be dose limiting and life altering. Rarely, TKIs can be associated with severe AEs such as pulmonary hemorrhage, fistula development, congestive heart failure, QTc prolongation, and death. Calculation of the calcitonin and CEA doubling time can help identify appropriate patients for targeted treatments who have more aggressive disease and poorer prognosis ( 101 ). A meta-analysis of evaluating calcitonin and CEA changes over time and recurrence-free survival found that doubling times (DTs) of 0 to 1 year were highly predictive of MTC recurrence and poor survival compared with DTs >1 year ( 102 ). CEA DT appears to have a higher predictive value than calcitonin DT. The ATA developed a calculator of the CT and CEA DT to assist clinicians in risk stratifying their patients ( 103 ). Case 2-1: Indolent Hereditary MTC without Systemic Therapy A 48-year-old woman with MEN-2A initially presented at the age of 20 years with medullary thyroid carcinoma proven by neck mass biopsy. Her baseline calcitonin was 299 pg/ml, and her CEA was ng/ml. After her total thyroidectomy, she was found to have residual disease radiographically, and she underwent right neck dissection 1 year later. She was found to have a right adrenal mass 21 years later. Although she was asymptomatic without any symptoms suggestive of pheochromocytoma, her biochemical testing revealed elevated plasma metanephrines. She underwent a right laparoscopic adrenalectomy, which confirmed a 1-cm pheochromocytoma. Her RET mutational testing was done at that time and identified a 634 codon mutation. She has never developed primary hyperparathyroidism, nor has there been any recurrence of pheochromocytoma in the right adrenal bed or on the contralateral side. After her right neck dissection over 20 years ago, she continued to have detectable calcitonin and CEA levels. Her staging studies performed at the time of her adrenalectomy identified multiple subcentimeter hepatic and vertebral spine lesions consistent with metastases. Over the last 8 years of surveillance, these 64 Translational Endocrinology & Metabolism: Neoplasia Update

21 lesions have demonstrated slight progression without development of symptoms. Her calcitonin and CEA have slowly progressed; the most recent levels are 2,624 pg/ml and 33.4 ng/ml, respectively. Her calcitonin DT is 24 years, and her CEA DT is 5.38 years per the ATA calculator. Although the patient understands the full extent of her disease and the clinical development of various targeted therapies for progressive or symptomatic MTC, she is comfortable with the recommendation to continue surveillance without any medical management. Resistance or nonsustainable partial responses to TKIs can be seen in Case 2-2. Carlomagno et al found that a mutation of valine 804 (V804M or V804L) in RET is associated with resistance to the effects of PP1 (pyrazolo-pyrimidine 1), PP2, (pyrazolo-pyrimidine 2) and vandetanib ( 82 ). A V804 mutation is found in approximately 2% of carriers of MEN-2 (germline mutation) and of sporadic (somatic mutation) MTC ( 104 ). Trials of TKIs in MTC have so far not detected any differential tumor response related to mutational status; the 2 phase 2 vandentanib studies for hereditary MTC did not enroll any patients with a V804M mutation. Eventual progression despite antiangiogenesis via VEGFR blockade raises the possibility of promoting alternate means to escape the inhibitory action of antiangiogenic agents, such as FGFR, c-met, and angiopoietins arising from hypoxia induction ( 53, 60 ). Development of agents that target the critical mediators of oncogenesis with greater specificity may improve the response rates and duration of response. Case 2-2: Progression after Initial Partial Response to TKI Management A 45-year-old man with MEN-2A presented 6 years ago with a right neck nodule, which was biopsy-proven as a metastatic focus of MTC to the lymph node. His baseline calcitonin was approximately 16,000 pg/ml with an unknown CEA and normal 24-hour urinary metanephrines. He underwent a total thyroidectomy with central neck dissection and right modified neck dissection, which confirmed multifocal MTC, C-cell hyperplasia, and metastatic lymphadenopathy in the central and right lateral compartments. His postoperative calcitonin reached a nadir of 800 pg/ml. His RET mutational analysis identified a V804M mutation. Due to continued rise of calcitonin over the next 2 years, he underwent a right radical superior mediastinal lymph node dissection for residual disease. Over a year later, with progressive calcitonin and CEA levels, a fine needle aspiration biopsy of a left thyroid bed nodule identified Multiple Endocrine Neoplasia Type 2 65

22 MTC. His calcitonin and CEA were 69,800 pg/ml and 903 ng/ml, respectively, and radiographic imaging of the liver and spine showed multiple lesions consistent with metastases, in addition to cervical adenopathy. He was clinically symptomatic, with diarrhea of 6 to 8 bowel movements a day and weight loss. As he had progression of calcitonin and CEA within 6 months, he was consented and enrolled into a clinical trial with single-agent TKI. He had a confirmed PR after 6 cycles of treatment with a decline of his calcitonin and CEA from baseline of 30% and 38%, respectively. Additionally, his diarrhea frequency declined and his weight had improved. Non-dose limiting side effects included change in taste, nausea, fatigue, and hair color hypopigmentation. Twenty months after initiation of the study treatment, he had progressive bone and hepatic lesions beyond his nadir measurements during the study. After discontinuation from that TKI trial, he was enrolled into a phase 1 study of sorafenib and bevacizumab (a monoclonal inhibitor of VEGFR) and has demonstrated stable disease with this combination. Differential responses in sites of metastases to TKI treatment have been recognized with the use of these drugs for other solid tumors, with lung being more responsive and bone being least susceptible ( 105, 106 ). Although the reason for this is not clear, there may be differential tissue distribution of drugs or the presence of other microenvironmental factors that can influence tumor growth not targeted by these drugs or that may prevent drug action. As bone metastases in MTC patients, often negatively affecting quality of life by leading to pain, fractures, or neuropathy, treatments that can target bone tumor progression are needed. For now, treatments are limited to bisphosphonates, external beam radiotherapy, or targeted radio-embolization to prevent skeletal-related events. Despite the potential challenges with using TKI therapy, there are significant benefits: sustainable disease control seen in many patients (see Case 2-3), availability of treatment options that provide hope for patients with progressive MTC, and continuous development of more effective agents as the knowledge base expands regarding oncogenic pathways. Case 2-3: Prolonged Durable Response with TKI Management A 41-year-old woman with MEN-2A with a codon 634 mutation was diagnosed with MTC when she was 19 years old when she had a right 66 Translational Endocrinology & Metabolism: Neoplasia Update

23 lobectomy for a thyroid mass. Two years later, she had a completion thyroidectomy due to continued elevations of calcitonin. Persistent increase in calcitonin led to the identification of recurrent disease in cervical lymph nodes; thus, bilateral neck dissection was performed. Over the course of the next 7 years, she had rising calcitonin and CEA and was found to have progressive hepatic metastases. She was enrolled in the phase 2 trial of vandetanib 300 mg/d dose. Her calcitonin and CEA at time of study enrollment were 160 pg/ml and 4.2 ng/ml, respectively. She had 1 target lesion in her liver (1 cm) and 2 subcentimeter nontarget lesions. During treatment, there was a 20% decrease in the size of the target lesion and disappearance of the 2 nontarget lesions. Due to individual AEs of hypokalemia, nausea with diminished renal function, and pleural effusion with pneumonia, her dose was reduced 3 times within the first 6 months of study initiation, and she has been maintained on 100 mg every other day for the last 5 years without further dose-limiting AEs and with continued stable disease. This case highlights the potential for long-term treatment of MTC with vandetanib and other TKIs, albeit at lower than initially recommended doses. It also points out the difficulty of determining longterm benefit in a patient with slowly progressive disease. The authors have concluded this patient benefitted from treatment because of the continued lack of growth of the target lesion over a 5-year period of observation and the complete and continued disappearance of 2 nontarget lesions and the lack of development of other new metastatic lesions. It is indeed somewhat surprising that the dose of 100 mg every other day, one that has no identifiable AEs, has stabilized her disease. Case 2-4: Sporadic MTC with a Somatic Codon M918T RET Proto-oncogene Mutation and Progressive Metastatic Disease This 52-year-old white Hispanic woman underwent total thyroidectomy at age 38 for a thyroid nodule and was found to have MTC with local nodal metastasis. Subsequent evaluation failed to identify distant metastatic disease, and later that year she underwent bilateral neck lymph node dissection with the identification of metastasis in 43 of 49 lymph nodes and extension of tumor into fibroadipose tissue. DNA sequence analysis of the metastatic tumor identified an M918T mutation of the RET proto-oncogene without evidence of a mutation in peripheral blood. Because of the extensive metastatic disease in the neck, she underwent external beam radiation therapy in her neck and upper mediastinum. Multiple Endocrine Neoplasia Type 2 67

24 Collective Diameter of Target Lesions (mm) Placebo Vandetanib % Reduction Jun-07 Jan-08 Aug-08 Feb-09 Sep-09 Mar-10 Oct-10 Apr-11 Nov-11 Date Calcitonin (pg/ml) Or CEA (ng/ml) Placebo Vandetanib Jun-07 Jan-08 Aug-08 Feb-09 Sep-09 Mar-10 Oct-10 Apr-11 Nov-11 Date FIG 2-2. Case 2-4. The upper panel shows the Response Evaluation Criteria in Solid Tumors response (total sum of diameters of target lesions in liver) for this patient while on placebo and after initiation of vandetanib therapy, showing a reduction of 40% following approximately 14 months of vandetanib therapy. The lower panel shows serum calcitonin and carcinoembryonic antigen (CEA) levels during the period of treatment with placebo and following initiation of vandetanib therapy. The small increase of serum calcitonin and CEA following initiation of vandetanib therapy may be an indication of tumor necrosis leading to release of preformed calcitonin and CEA. Over the next 10 years she developed progressive metastatic disease in lung, liver, and bone. At age 47, she entered a prospective randomized placebo-controlled trial of vandetanib. It was subsequently learned when she developed evidence of progressive disease in a nontarget lesion that she was being treated with placebo. She subsequently elected to be treated with vandetanib and was started on vandetanib 300 mg/d ( Figure 2-2 ). This was subsequently reduced to 200 mg/d 6 months after 68 Translational Endocrinology & Metabolism: Neoplasia Update