The skin is the second most common extranodal site for

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1 CAP Laboratory Improvement Programs Best Practices in Diagnostic Immunohistochemistry Workup of Cutaneous Lymphoid Lesions in the Diagnosis of Primary Cutaneous Lymphoma Rajan Dewar, MD, PhD; Aleodor Alexandru Andea, MD; Joan Guitart, MD; Daniel A. Arber, MD; Lawrence M. Weiss, MD Context. Primary cutaneous lymphoma is a common extranodal non-hodgkin lymphoma. These lesions share common features with their nodal counterparts, but also have differences in morphology, unique clinical presentations, and immunohistochemical features. Objective. To review the 2008 World Health Organization (WHO) and 2005 consensus WHO-EORTC (European Organisation for Research and Treatment of Cancer) classifications, and address the immunohistochemical findings in the most common primary cutaneous T- and B-cell lymphomas. Since clonality testing is commonly used as an ancillary test in the evaluation of cutaneous lymphoma, a brief section in the use and pitfalls of clonality testing is included. Data Sources. The WHO and EORTC classification publications and the relevant recent literature were used to compile appropriate and practical guidelines in this review. Conclusions. The practice of dermatopathology and hematopathology varies widely. Thus, while this review provides an overview and guideline for the workup of lymphoid lesions of the skin, the practitioner should understand the importance of clinical correlation as well as appropriate utility of available resources (such as clonality testing) in arriving at a diagnosis in cutaneous lymphoid lesions. (Arch Pathol Lab Med. 2015;139: ; doi: / arpa cp) The skin is the second most common extranodal site for non-hodgkin lymphoma after the gastrointestinal tract. Primary cutaneous lymphomas comprise a diverse group of distinct lesions, arising from T cells or B cells. Accurate diagnosis and classification is essential in the prognosis and management of primary cutaneous lymphoma, and immunohistochemistry (IHC) plays an integral role. Primary cutaneous lymphomas are defined as lymphomas that arise in or involve primarily the skin, with little or Accepted for publication May 9, From the Department of Pathology, Beth Israel Deaconess Medical Center, and Harvard Medical School, Boston, Massachusetts (Dr Dewar); the Department of Pathology, University of Michigan, Ann Arbor (Dr Andea); the Department of Pathology and Dermatology, Northwestern University, Chicago, Illinois (Dr Guitart); the Department of Pathology, Stanford University Medical Center, Stanford, California (Dr Arber); and the Department of Hematopathology, Clarient Pathology Services, Inc, Aliso Viejo, California (Dr Weiss). The authors have no relevant financial interest in the products or companies described in this article. This article is provided for educational purposes only and is not intended to suggest either a practice standard or the only acceptable pathway for diagnostic evaluation. The views presented reflect the authors opinions. The application of these opinions to a particular medical situation must be guided by the informed medical judgment of the responsible pathologist(s) on the basis of the individual circumstances presented by the patient. The College of American Pathologists has no responsibility for the content or application of the views expressed herein. Reprints: Rajan Dewar, MD, PhD, Department of Pathology, Beth Israel Deaconess Medical Center, 330 Brookline Ave., Boston, MA ( rdewar@bidmc.harvard.edu). limited extracutaneous spread at the time of diagnosis. Since skin involvement may rarely be the primary manifestation of nodal or extracutaneous nonnodal lymphoma, thorough staging integrating radiologic, clinical, and other laboratory information (including a peripheral smear and/or bone marrow) is essential to rule out a systemic lymphoma with secondary cutaneous involvement. The current classification of cutaneous lymphoma is a result of efforts by the European Organisation for Research and Treatment of Cancer (EORTC) and the World Health Organization (WHO). 1 The EORTC classification of 1997 was the first comprehensive modern classification of cutaneous lymphoma. 2 The WHO classification of hematopoietic neoplasm in included cutaneous lymphoma and included some variants of systemic lymphoma as they specifically involved the skin. Both authorities (WHO and EORTC) combined their respective classifications, and the WHO-EORTC classification scheme was published in The last WHO classification of lymphomas released in incorporated the cutaneous lymphomas as separate entities and is currently the most extensive as well as that most frequently followed by dermatologists and pathologists. The list of lymphoma entities is comprehensive (Table 1), although some of the entities are still provisional (eg, primary cutaneous CD4 þ small/medium-sized T-cell lymphoma). Immunohistochemistry plays an important role in the classification of primary cutaneous lymphoma, based on the WHO-EORTC. The purpose of this review is to serve as a practical guide for the utilization of immunohistochemical stains in the classification of primary cutaneous lymphoma. 338 Arch Pathol Lab Med Vol 139, March 2015 IHC in Cutaneous Lymphoma Dewar et al

2 Table 1. World Health Organization (WHO) (2008) 5 and WHO-EORTC (2005) 4 Classification of Primary Cutaneous Lymphoma Primary cutaneous lymphoma of T-cell and NK-cell lineage Mycosis fungoides Sezary syndrome Adult T-cell leukemia/lymphoma Primary cutaneous CD30 þ T-cell lymphoproliferative disorders Primary cutaneous anaplastic large cell lymphoma Lymphomatoid papulosis Subcutaneous panniculitis-like T-cell lymphoma Extranodal NK-/T-cell lymphoma, nasal type Primary cutaneous peripheral T-cell lymphoma, unspecified Primary cutaneous lymphoma of B-cell lineage Primary cutaneous marginal zone B-cell lymphoma a Primary cutaneous follicle center cell lymphoma Primary cutaneous diffuse large B-cell lymphoma, leg type Primary cutaneous diffuse large B-cell lymphoma, others Other entities: precursor hematologic neoplasm Blastic plasmacytoid dendritic cell neoplasm Abbreviations: EORTC, European Organisation for Research and Treatment of Cancer; NK, natural killer. a Included in extranodal marginal zone lymphomas in WHO 2008 classification. This comprehensive review will cover the most common B- and T-cell primary cutaneous lymphomas; rare entities, unusual limitations, and details of individual antibody clones or exceptions will not be discussed. THE ROLE OF MORPHOLOGY IN THE INITIAL WORKUP OF CUTANEOUS LYMPHOID LESIONS Clinical and morphologic criteria play a very important role in the subclassification of cutaneous lymphoid lesions. 6 The presence or absence of multiple sites of involvement, antecedent history, peripheral blood involvement, tempo and pattern of progression (aggressive or chronic), and association with other local or systemic diseases (contact dermatitides or autoimmune disease such as lupus) are important considerations not only for the diagnosis but also to distinguish the lesion from pseudolymphoma (reactive lymphoid proliferations that very closely mimic lymphoma). In addition, many types of cutaneous lymphoma can have similar histomorphologic features for example, some tumoral lesions of mycosis fungoides (MF) with large cell transformation cannot be reliably distinguished from anaplastic large cell lymphoma or lymphomatoid papulosis by hematoxylin-eosin sections or even IHC. Thus, clinical correlation is very important in the accurate diagnosis and classification of cutaneous lymphoma, much more so than in the diagnosis of other extranodal or nodal lymphomas. For optimal morphologic assessment, sections should be 4 to 5 lm. A low-magnification examination should be first performed to assess the architecture of the infiltrate (superficial, superficial and deep, deep or subcutaneous), distribution (perivascular, interstitial, diffuse or nodular), and involvement of epithelial structures (epidermotropism, appendageal structures eg, pilotropism or syringotropism). This examination should be followed by an intermediatemagnification assessment to look for cellular composition (monomorphous versus mixed population; presence of other inflammatory cells) and other features (eg, presence of mucin, angioinvasion, destruction). A high-magnification assessment of the cellular morphology is then performed to evaluate features such as cellular shape, cytoplasm, nuclearcytoplasmic ratio, nuclear contours, and nuclear chromatin. The above morphologic clues will provide the basic framework for the selection of appropriate antibody panels. For example, a superficial diffuse dermal infiltrate with extensive epidermotropism and epidermal microabscesses is most likely to be a T-cell lymphoid proliferation. In contrast, a deep or superficial and deep dermal infiltrate with a nodular pattern is likely to be a B-cell lymphoid proliferation. Nonetheless, at times when this distinction is difficult, a screening panel should be used; this panel could include B-cell markers such as CD20, T-cell markers such as CD3, and CD30 (to identify CD30 þ lymphoproliferative disorders), and may be useful to provide an initial indication as to lymphocyte lineage. An overview of T-cell marker utilization is given below (also see Table 2); B-cell markers will be described within individual entities (also see Table 3). T-cell abnormalities are best characterized by immunohistochemical stains for T-cell specific antigens (Table 2). Normal T cells show expression of pan T-cell antigens (most commonly CD2, CD3, CD5, and CD7). Precursor stage differentiation within the thymus will give rise to CD4 (also called helper) and CD8 (also called cytotoxic) subset of T cells. All T cells express either CD4 or CD8 except for rare cd cells that lack both CD4 and CD8. Loss of any of the pan T cell antigens, as well as coexpression of both CD4/CD8 (so-called double positive) or lack of both CD4/CD8 (socalled double negative), are considered abnormal, indicating a lymphoproliferative process, but may be seen rarely in reactive conditions, particularly autoimmune disorders such as lupus 7 or rheumatoid arthritis. 8 Along with these antigenic markers, T cells also undergo rearrangements of the T-cell receptor genes, resulting in unique cell surface receptors (T-cell receptors; TCRs). T-cell receptors are of 2 types. Most circulating T cells (representing 95% or greater of peripheral blood T cells) and tissue T cells express ab type, with the remainder belonging to the cd T-cell subtype. The immunohistochemical profile of an ab T-cell and a cd T-cell is distinguished most often by a single antigen recognized by antibody clone bf1. This antibody clone bf1 maps to an epitope within the constant region of the b chain of T-cell receptor, present only within ab T cells, not seen in cd T cells, and can be identified in paraffin sections by routine IHC. 9 Newer antibodies that cover the c and d epitopes have been developed in recent years, but are not widely used yet. For example, an antibody to the TCR d epitope has been described recently, 10 but the experience with it is relatively limited. T-cell receptor c (TCRG or c-m1) is available commercially. 11,12 CUTANEOUS T-CELL LYMPHOID PROLIFERATIONS Mycosis Fungoides and Sezary Syndrome Mycosis fungoides is the most common cutaneous T-cell lymphoma. 13 It has 3 distinct clinical stages (patch, plaque, and tumor). Most cases of typical MF are chronic, slowly evolving lesions with a long-standing course. Lymphomas with similar histomorphology but aggressive clinical course are usually classified in other categories (eg, cytotoxic T-cell/ natural killer [NK] cell lymphoma). Mycosis fungoides is characterized by a proliferation of small to medium-sized pleomorphic lymphocytes and often by prominent epidermotropism. The nuclear contours of the lymphocytes are convoluted and can be appreciated in MF cells circulating in Arch Pathol Lab Med Vol 139, March 2015 IHC in Cutaneous Lymphoma Dewar et al 339

3 Table 2. Immunophenotypic Profile of Cutaneous T-Cell Lymphomas Entity CD2 CD3 CD4 CD5 CD7 CD8 CD30 CD56 Cytotoxic Molecules a bf1 PD-1 EBV CD123 TCR MF þ þ þ þ /þ b /þ c /þ d þ /þ e þ SCPTCL þ þ /þ /þ þ þ þ NA þ C-ALCL þ/ þ þ þ/ þ/ þ þ þ NA þ LyP þ/ þ þ þ/ þ/ f þ g þ þ NA þ PCGD þ þ /þ /þ þ þ NA þ PCAE CD8 þ TCL /þ þ þ þ þ þ NA þ PC CD4 þ SM þ þ þ þ/ þ/ þ þ þ ENKTCL þ h /þ /þ þ þ NA þ BPDCN i þ þ NA þ Abbreviations: BPDCN, blastic plasmacytoid dendritic cell neoplasm; C-ALCL, cutaneous anaplastic large cell lymphoma; EBV, Epstein-Barr virus; ENKTCL, extranodal NK-/T-cell lymphoma, nasal type; LyP, lymphomatoid papulosis; MF, mycosis fungoides; NA, not available; PC CD4 þ SM, primary cutaneous CD4 þ small/medium-sized T-cell lymphoma; PCAE CD8 þ TCL, primary cutaneous aggressive epidermotropic CD8 þ T-cell lymphoma; PCGD, primary cutaneous cd T-cell lymphoma; PD-1, programmed death 1; SCPTCL, subcutaneous panniculitis-like T-cell lymphoma; TCR, T-cell receptor gene rearrangements. a Includes TIA-1, granzyme B, and perforin. b CD8 þ phenotype may occur in pediatric patients and is characteristic for pagetoid reticulosis variant of MF. c CD30 shows positivity in pagetoid reticulosis variant of MF but can also be seen in plaque of tumor-stage MF or in MF with large cell transformation. d Cytotoxic markers can show positivity in advanced cases. e PD-1 is expressed by Sezary cells. f A CD8 þ phenotype has been recently described as type D LyP. g CD56 may show positivity in rare cases. h Cytoplasmic CD 3e shows positivity. i BPDCN is not considered a T-cell lymphoma in the 2008 World Health Organization classification but is included here for differential diagnosis consideration. the peripheral blood (sometimes referred to as cerebriform ). Collections of intraepidermal lymphocytes termed Pautrier microabscesses (originally described by Pautrier as Darier nests) are considered characteristic (Figure 1, A) but are seen only in a minority of lesions, usually patch and plaque stage. The epidermotropic lymphocytes have slightly enlarged nuclei compared to the intradermal lymphocytes and may show a convoluted nuclear contour (Figure 1, B). These cells are approximately the size of the nucleus of an epithelial cell. The presence of lymphocytes aligned along the basal layer of the epidermis is a useful histologic feature to recognize. In advanced-tumor-stage lesions the epidermotropism and the Pautrier microabsceses are often absent. Interstitial fibrosis, most commonly seen in the upper dermis as bands of fibrosis interrupted by abnormal lymphocytes ( fettuccine fibrosis ), is a common finding in MF. Other histologic features may include psoriasiform epidermal hyperplasia and presence of intraepidermal mucin sometimes mimicking an inflammatory process. There is usually little or no epidermal spongiosis. In the cases with spongiosis there is a disproportionate amount of lymphocytic epidermotropism relative to the degree of spongiosis. Some cases of MF may not need immunohistochemical characterization, if the histomorphology and clinical features are characteristic. In cases with less definitive histology, and if the clinical history is not reliable or not consistent with MF, immunohistochemical studies may be performed. Mycosis fungoides is characterized by T cells with ab T- helper memory phenotype. Their typical immunohistochemical profile is CD3 þ, bf1 þ, CD4 þ, CD5 þ and CD8. Often there is aberrant loss of CD7. An initial IHC profile demonstrating a CD3 þ lymphocytic population (Figure 1, C) with an increased CD4:CD8 ratio is helpful in establishing a diagnosis. 14,15 A high epidermal CD4:CD8 ratio (averaging 3.5) has been associated with MF. The ratio was lower in Table 3. Immunophenotypic Profile of Cutaneous B-Cell Lymphomas CD20/CD79a/ Entity PAX5 CD5 CD10 BCL2 BCL6 HGAL IGLC CD21 MUM-1 FOXP1 CD3 PD-1 PCMZL þ a þ a a þ b c d PCFCL þ þ e f þ þ g NA DLBCL-L þ þ þ þ þ NA BCPL þ þ h /þ i þ h þ h h þ Abbreviations: BCPL, B-cell pseudolymphoma; DLBCL-L, diffuse large B-cell lymphoma, leg type; HGAL, human germinal center associated lymphoma antigen; IGLC, immunoglobulin light chains; NA, not available; PCFCL, primary cutaneous follicle center lymphoma; PCMZL, primary cutaneous marginal zone B-cell lymphoma; PD-1, programmed death 1. a Negative in the lesional cells but highlights the associated reactive germinal centers. b Light-chain restriction can be demonstrated in the plasma cell population, which helps to differentiate from B-cell pseudolymphoma. c Negative in the lesional cells but CD21 highlights the distorted dendritic meshwork of the associated germinal centers, which helps to differentiate from B-cell pseudolymphoma. d Negative in the lesional cells but highlights a population of reactive T cells. e CD10 may show negativity in cases with diffuse growth pattern. f BCL2 can show positivity in rare cases. g Negative in the lesional cells but CD21 highlights the dendritic meshwork of the neoplastic germinal centers. h Highlights reactive germinal centers. i Negative in the reactive germinal centers but positive in the associated T cells. 340 Arch Pathol Lab Med Vol 139, March 2015 IHC in Cutaneous Lymphoma Dewar et al

4 Figure 1. A, Pautrier microabscess in a patient with mycosis fungoides. B, Cytomorphology of mycosis fungoides. The irregular and convoluted nuclei in small to medium-sized cells are characteristic. C, CD3 immunostaining confirms the T-cell origin of these cells. If inconspicuous, CD3 also highlights the epidermal microabscesses (hematoxylin-eosin, original magnifications 3400 [A] and [B]; original magnification 3400 [C]). atypical (1.6) and benign (1) cases in this study. Doublepositive and double-negative (CD4 and CD8) MFs have been described. 16,17 CD8 þ MFs tend to occur in pediatric cases and in hypopigmented variant lesions, and are prognostically similar to the usual CD4 þ MFs. 18,19 Mycosis fungoides in plaque or tumor stage or with large cell transformation may have increased numbers of CD30 þ cells. Cytotoxic markers such as TIA-1 may show positivity in advanced stages. Very rarely, these T cells may aberrantly express CD20 or CD79a, 20 but typically do not express other B-cell antigens such as PAX5. Sezary syndrome is a rare disease characterized by erythroderma, lymphadenopathy, and a neoplastic T-cell population involving skin, lymph nodes, and peripheral blood. Cutaneous lesions of Sezary syndrome share many of the histologic features of mycosis fungoides, and in the United States, MF and Sezary syndrome are often combined together into 1 entity. The WHO 2008 classification distinguishes these as 2 separate entities. In the EORTC scheme, peripheral blood involvement in a patient with MF is not distinguished as Sezary syndrome, even though some pathologists preferentially note this as Sezary syndrome preceded by MF, and distinct chromosomal changes have been observed in these cases. The primary distinguishing feature of Sezary syndrome is the presence of blood involvement; however, the diagnosis (which leads to treatment decisions and further defines clinical end points) of Sezary syndrome requires a set of specific criteria, 21,22 as listed in Table 4. Peripheral blood often shows mediumsized Sezary cells, with convoluted cerebriform nuclei, similar to those seen in tissues. The tumor cells have a CD3 þ, CD4 þ, and CD8 phenotype similar to MF. Often, these peripheral blood cells show loss of T-cell antigens, most commonly CD7 and CD26 23 (demonstrable by flow cytometry), but may also show loss of CD2, CD3, CD4, and CD5. Expression of the antigen PD-1 (programmed death 1) is reported as a reliable marker of Sezary cells. 24 Of note, PD-1 is a marker of T-helper cells of follicle origin and is seen in other T-cell lymphomas such as angioimmunoblastic T-cell lymphoma and a subset of peripheral T-cell lymphoma, not otherwise specified. 25 Primary Cutaneous CD30 þ T-Cell Lymphoproliferative Disorders Primary cutaneous CD30 þ T-cell lymphoproliferative disorders 26,27 are among the commonest cutaneous T-cell lymphomas (second to MF), accounting for about 30% of all cases and encompassing 3 diseases: lymphomatoid papulosis (LyP), cutaneous anaplastic large cell lymphoma (C- ALCL), and borderline cases. Despite demonstrable clonality, LyP is not considered a fully malignant disorder, whereas C-ALCL is regarded as bona fide T-cell lymphoma. 28 The borderline cases share clinical and morphologic features with the 2 distinct entities. 29 Of note, clinical findings are very important in distinguishing between C- ALCL and LyP, since morphology, immunophenotype, and clonality studies alone are not enough to distinguish between these 2 entities, in some cases. The histology of C-ALCL often shows a diffuse proliferation of medium to large anaplastic cells, usually sparing the epidermis. The neoplastic infiltrate is typically composed of large cells that show variable pleomorphism, sometimes interspersed with mononuclear Hodgkin-like cells (Figure 2, A). The nuclear contours are often described as wreathlike ; the medium-sized anaplastic cells that have abundant, clear, eosinophilic or amphophilic cytoplasm, with a kidneyshaped nucleus and an eosinophilic paranuclear region, are termed hallmark cells. The infiltrate may be dominated by neutrophils or may show panniculitis-like changes, especially in immunosuppressed patients. 30,31 The lesional cells are by definition CD30 þ, which is expressed by a majority (.75%) of the neoplastic infiltrate (Figure 2, B). They are usually CD3 þ, CD4 þ, and CD8. Unlike Hodgkin lymphoma cells, they are CD15 and do not express PAX5. Arch Pathol Lab Med Vol 139, March 2015 IHC in Cutaneous Lymphoma Dewar et al 341

5 Table 4. Diagnostic Criteria for Sezary Syndrome Significant erythroderma Demonstrating a clonal T-cell population in blood; T-cell gene rearrangement studies by PCR Absolute peripheral blood Sezary cell count:.1000 Sezary cells/ll Alternatively, an increased CD4/CD8 ratio of more than 10 (or) increased CD4 count with an abnormal phenotype (CD4 þ /CD7 or CD4 þ /CD26 ) Abbreviation: PCR, polymerase chain reaction. Lymphomatoid papulosis shares the exact antigenic profile of C-ALCL, with CD4 þ CD8 expression and also expression of CD30. Three common histologic patterns have been classically described (types A, B, and C) with a fourth one (type D) being added recently. 29 Of the three, type B resembles MF and can show extensive epidermotropism. Of note, in type B LyP, the cells are frequently CD30. Rare cases of both C-ALCL and LyP can express CD56 and other NK cell markers. The fourth pattern characteristically is of a CD8 phenotype with pagetoid changes. 32,33 About a third of LyPs or CD30 þ lymphoproliferative disorders express cytotoxic markers such as TIA Subcutaneous Panniculitis-like T-Cell Lymphoma In the most recent classification, subcutaneous panniculitis-like T-cell lymphoma is recognized as a rare form of primary cutaneous T-cell lymphoma with distinct morphologic and immunohistochemical features. Subcutaneous panniculitis-like T-cell lymphoma (SPTCL) preferentially involves the subcutaneous fat in a lobular pattern. Fat necrosis, karyorrhexis, and admixed histiocytes with vacuolated cytoplasm, containing apoptotic debris and erythrocytes, are commonly seen (Figure 3, A), and this may superficially mimic other reactive conditions, such as lupus. 35,36 The lymphocytes are small to medium, have irregular nuclei, and often show rimming around individual fat cells (Figure 3, B). In the WHO 2008 and EORTC classification, this entity is restricted only to the ab T cells. The characteristic immunohistochemical profile 37 is CD3 þ, CD8 þ (Figure 3, C and D), with expression of cytotoxic markers (including granzyme-b, TIA-1, and perforin) and of a/b receptor (Figure 3, E). CD56 usually shows negativity. Those lesions with predominantly cd T cells (bf1 ) are considered an entity separate from SCPTCL owing to their significantly worse prognosis and are classified as cutaneous cd T-cell lymphoma (see below). Primary Cutaneous Peripheral T-Cell Lymphomas, Rare Subtypes Primary Cutaneous cd T-Cell Lymphoma. These lymphoproliferative lesions with a cd phenotype are clinically aggressive 38 (median survival of ~15 months) and consist of activated cytotoxic T cells with variable morphology. The variability in morphology is described within 3 major histologic patterns primarily epidermotropic, dermal, and subcutaneous. 10 The neoplastic cells are medium to large with elongated or folded nuclei and show frequent mitotic activity. The tumor cells are T cells that express CD3 (Figure 4, A) and CD2. They show loss of CD5 (Figure 4, B) or CD7. The cytotoxic proteins (TIA-1 and granzyme) are expressed, as is CD56 (Figure 4, C). The cells can show loss of CD4 (Figure 4, D) and CD8 (Figure 4, E). A subset of cases is CD8 þ but only rare cases express CD4. Figure 2. Primary cutaneous CD30 þ T-cell lymphoma. A, Note the cellular pleomorphism with anaplastic cells. Hodgkin-like cells are commonly seen (hematoxylin-eosin). B, CD30 immunostaining, by definition, is positive in the neoplastic T cells. The cells are also CD3 þ and CD4 þ and lack CD8. Some cells show a perinuclear dotlike positivity at the Golgi apparatus, as may be seen in classical Hodgkin cells (original magnification 3400 [A and B]; original magnification 3400 [B]). CD30 and Epstein-Barr encoded RNA expression may be seen in rare cases. The cells are of the TCR-cd phenotype, by definition. When available, this phenotype can be demonstrated by IHC staining for TCR-d or TCR-c (Figure 4, F) with appropriate detection methods. However, in routine practice, so far, absence of bf1 expression (Figure 4, G) is considered an inferential surrogate for the cd phenotype. Primary Cutaneous Aggressive Epidermotropic CD8 þ T-Cell Lymphoma Also known as Berti lymphoma, this is an aggressive T-cell lymphoma with a cytotoxic phenotype. 39,40 The histology and neoplastic cytomorphology are frequently indistinguishable from other epidermotropic T-cell lymphoproliferative disorders such as CD8 þ variants of MF, pagetoid variants of cutaneous cd T-cell lymphoma, or type D LyP. 10,32 Distinction from other CD8 þ T-cell lymphomas with epidermotropism is based mostly on clinical presentation. Unlike conventional MF, the cells are CD8 þ and unlike cd T-cell lymphoma, the neoplastic cells express bf1, indicating an ab-tcr pheno- 342 Arch Pathol Lab Med Vol 139, March 2015 IHC in Cutaneous Lymphoma Dewar et al

6 Figure 3. Subcutaneous panniculitis-like T-cell lymphoma (SPLTCL). A, This atypical lymphoid infiltrate involves the dermis and subcutis, composed of medium-sized cells. Note the presence of single cell necrosis and karyorrhectic debris. B, Fat necrosis and rimming of the atypical cells around the adipocyte are not uncommon. C, The T cells typically express CD3. D, The T cells typically coexpress CD8. E, The T cells of SPLTCL are of the ab phenotype (T-cell receptor ab). The use of immunostains targeting the b epitope (clone bf1) is helpful in distinguishing ab T cells from the cd type (hematoxylin-eosin, original magnifications 3100 [A] and 3200 [B]; original magnifications 3200 [C and D]; peroxidase, original magnification 3200 [E]). Arch Pathol Lab Med Vol 139, March 2015 IHC in Cutaneous Lymphoma Dewar et al 343

7 344 Arch Pathol Lab Med Vol 139, March 2015 IHC in Cutaneous Lymphoma Dewar et al

8 type. Thus, the neoplastic cells of this entity are CD3 þ, bf1 þ, CD7 þ,cd8 þ with cytotoxic proteins (TIA-1 and granzyme). CD7 is usually preserved among the T cells. Among the pan T-cell antigens there is variable loss of CD2, and, more frequently, loss of CD5 may be seen. The median survival of patients, as originally described in the Berti series, 40 is approximately 32 months. Primary Cutaneous CD4 þ Small/Medium-Sized Pleomorphic T-Cell Lymphoma This is a new and provisional entity in the WHO-EORTC. 5 It is usually a solitary lesion, reported mostly in the head and neck region. Most of the lesion is composed of small to intermediate atypical cells (Figure 5, A and B) that are positive for CD4 and lack CD8 or other cytotoxic markers. 10 Antigenic loss or aberrancy is only rare. More recently, PD-1 expression, a marker of follicular T-helper cells, has been found in this entity. 25,41 A population of small reactive lymphocytes, histiocytes, and occasional eosinophils is usually noted. Since there are no major distinguishing features of this infiltrate from benign or reactive lymphoid population outside of cytologic features, clonality studies are usually helpful and should yield positive findings. The localized solitary lesions have a very good prognosis, with a 5-year survival rate of more than 75%. The correct classification of this entity as a true lymphoma or as a pseudolymphoma is still disputed. Extranodal Cutaneous NK-/T-Cell Lymphoma WHO-EORTC classification includes 4 distinct T- and NK-cell lymphomas that involve the skin as a secondary site. These are extranodal NK-/T-cell lymphoma, nasal type, hydroa vacciniforme-like lymphoma, adult T-cell leukemia/ lymphoma, and angioimmunoblastic lymphoma. 10 Since these are rare entities, or not primarily cutaneous, they are not described further in this review. PRIMARY CUTANEOUS B-CELL LYMPHOMAS Cutaneous Marginal Zone B-Cell Lymphoma Cutaneous marginal zone lymphoma 42,43 is a low-grade B- cell lymphoma composed of nodular or diffuse proliferation of small to medium-sized cells. These cells are classically described as monocytoid lymphocytes and may show conspicuous lymphoplasmacytic differentiation or be admixed with terminally differentiated plasmacytic cells (Figure 6, A). In practice, many lesions consist of small lymphoid cell infiltrate with no specific morphology, indicating a plasmacytic differentiation. Germinal centers are occasionally noted in the lesion, but they may be absent, less conspicuous, distorted, atrophic, or commonly, completely absent. The B cells are typically positive for CD20 (Figure 6, B), CD79a, and PAX5 (the B-cell markers may have variable intensities) and usually lack expression of CD5 and CD10. BCL2 expression is present, and the Ki-67 fraction is not very high in most of the lesions. CD21 stain is useful in highlighting the follicular dendritic cells of lymphoid follicles present in the lesion. The CD21 stains usually show distortion and dissolution of the dendritic cell meshwork, which supports a diagnosis of lymphoma. Follicular colonization is a distinctive feature observed in marginal zone lymphoma, appreciated with many of the immunohistochemical stains used. The presence of follicle center cells (BCL6 positive, BCL2 negative), which are infiltrated by the neoplastic marginal zone cells (BCL6 negative, BCL2 positive), is a useful clue for the diagnosis of marginal zone lymphoma. This impression may also be seen in immunostains for Ki-67, where the highly proliferative germinal center cells are infiltrated by neoplastic cells with a low proliferation index. A population of reactive CD3 þ T cells is often noted. PD-1 is conspicuously negative. Demonstration of light-chain expression is a very useful adjunct in evaluation of B-cell neoplasms (see also Table 3). j and k light-chain restriction by protein IHC is difficult to demonstrate, even in lesions that have a predominance of plasma cells; both j/k IHC (Figure 6, C and D) and in situ hybridization may be attempted to demonstrate proof of clonal restriction. If clear light-chain monotypia is present, then this supports a clonal process. However, absent or equivocal light-chain restriction does not exclude a diagnosis of lymphoma. Since a variety of reactive lymphoid proliferations can mimic lymphoma, 44 immunoglobulin (Ig) H clonality studies may need to be performed if light-chain restriction studies are not definitive. In a small subset of cases, Borrelia burgdorferi infections are associated as an antigenic stimuli of cutaneous B-cell lymphoma of the marginal zone type, particularly in European populations, but are neither necessary nor easy to demonstrate to make the diagnosis When demonstrated (usually by polymerase chain reaction), antibiotic therapy may be attempted, which is associated with cure of only a small subset of cases. 48 The t(11;18), which is usually seen in nodal marginal zone lymphomas, is not present in most cases of cutaneous marginal zone lymphoma. Primary Cutaneous Follicle Center Lymphoma Primary cutaneous follicle center lymphoma (PCFCL) differs significantly from systemic or nodal follicular lymphoma, which partially explains the challenges in the diagnosis. 5,42 The typical case of PCFCL is composed of small to intermediate-sized cells with classically cleaved nuclear contours (centrocytes) admixed with centroblasts. The similarity with nodal follicular lymphoma may end there. The presence of back-to-back follicles or nodules (as seen in the upper dermis of Figure 7, A) is not seen in many cases of PCFCL, where there may be confluence of nodules Figure 4. Primary cutaneous cd T-cell lymphoma. A, CD3 immunostaining showing T-cell profile. Note the periadipocytic infiltrate. A panel of immunostains is often necessary in characterizing primary cutaneous lymphoma, and the use of CD4 and CD56 helps in distinguishing this entity from subcutaneous panniculitis-like T-cell lymphoma. B, The pan T-cell antigen CD5 is commonly lost. C, Primary cutaneous cd T-cell lymphoma showing malignant lymphocytes expressing CD56 (neural cell adhesion molecule). D, CD4 is lost; loss of CD4 is very commonly seen. E, Primary cutaneous cd T-cell lymphoma showing loss of CD8. This is the same case as seen in (D). CD4 and CD8 both are aberrantly lost within T cells. A subset of cases may show CD8 expression, but CD4 expression is very rare. Cases with aberrant expression of both CD4 and CD8 have not been reported. F, Antibodies targeting cd (eg, T-cell receptor c [TCRG]) are not widely available yet and are at the early stages of clinical applications. G, The neoplastic T cells are negative for bf1. bf1 is an antigen present in the b chain of the TCR. Since cd T-cell lymphoma does not express b chain, absence of bf1 is presumptive evidence that the T cells have cd T-cell receptors. This antibody is more commonly used than the one targeting TCRG (original magnifications 3400 [A through G]). 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9 Figure 5. A, Primary cutaneous CD4þ small/medium-sized pleomorphic T-cell lymphoma. The lesion consists of a diffuse infiltrate of atypical lymphocytes (hematoxylin-eosin). B, The neoplastic T cells express CD4 and the infiltrate is composed of predominantly small to intermediate-sized lymphocytes with irregular nuclear contours and a blastlike appearance. The cells are positive for PD-1, a marker of follicular T-helper cells (not shown) (original magnification 3100 [A]; original magnification 3400 [B]). Figure 6. Primary cutaneous marginal zone lymphoma. A, Note the expanded follicles with a nodular proliferation of intermediate-sized cells with monocytoid appearance and lymphoplasmacytoid differentiation. The germinal centers are atrophic or inconspicuous (hematoxylin-eosin). B, The neoplastic B cells express CD20 variably; in this example, the B cells stain brightly for CD20. C and D, Proving the clonal nature of the infiltrate is very helpful. Here, j (C) and k (D) immunostaining show that the cells are j monotypic. In some instances, in situ hybridization for j and k is more helpful than j and k by immunohistochemistry (original magnification 3200 [A]; original magnifications 3400 [B through D]). 346 Arch Pathol Lab Med Vol 139, March 2015 IHC in Cutaneous Lymphoma Dewar et al

10 Figure 7. Primary cutaneous follicle center cells lymphoma. A, The neoplastic nodules are usually present in the deep dermis. They are composed of small to intermediate-sized cleaved cells centrocytes (hematoxylin-eosin). B, The neoplastic nodules are CD20 þ. C, BCL6 expression in primary cutaneous follicular lymphoma. Unlike nodalbased follicular lymphoma, the cells are frequently BCL2 negative and in some instances may not show CD10 positivity (original magnification 3100 [A]; original magnifications 3100 [B and C]). (bottom half of the biopsy specimen in Figure 7, A) or just diffuse effacement with B cells (Figure 7, B) with centrocyte morphology. BCL2 expression, classically seen and pathognomonic of most nodal follicular lymphomas, is lacking in most cases of PCFCL. Diagnosis of PCFCL requires the demonstration of germinal center associated markers within the neoplastic B cells. While CD10 is a commonly used marker and shows positivity in a subset of cases 49 with a follicular pattern, it may be lost in a good portion of PCFLCs and those with a diffuse growth. Other markers, including BCL6, human germinal center associated lymphoma (HGAL also known as GCET2) antigen, 50 or GCET1, may be used as alternatives. In summary, most PCFCLs are monoclonal B cells (typically demonstrated by IgH clonality studies) usually expressing BCL6 (Figure 7, C) but showing variable CD10 expression. BCL2 usually shows negativity or, when present, is faint (or in a subset of cells). 42 MUM-1 is not expressed in PCFCL. IGH/BCL2 translocation will be negative in most (59% 90%) cases. 42 The absence of BCL2 in most PCFCLs does not have prognostic implications. However, excluding secondary involvement of skin by systemic/nodal follicular lymphoma should be done in all cases with positive BCL2 expression, since this is more common. Primary Cutaneous Diffuse Large B-Cell Lymphoma, Leg Type This is an aggressive B-cell lymphoma that is usually, but not always, present in the lower limbs; it is more common in females and can be bilateral. 5,42 The lesion is typically composed of a monomorphic population of large centroblasts and immunoblasts with few admixed cells. Immunohistochemistry shows strong BCL2 expression. BCL6 usually shows positivity but CD10 is variably expressed. MUM-1/ IRF4 shows positivity (activated B-cell ABC profile). The strong BCL2 and MUM-1 expression distinguishes diffuse large B-cell lymphoma (DLBCL), leg type, from follicle center cell lymphoma (follicular lymphoma) with large cell transformation, in most cases. 42 IgM and HGAL as markers to aid in the differentiation between these 2 entities have been reported FOXP1 is shown to be expressed in most DLBCLs, leg type. 53 Primary Cutaneous Diffuse Large B-Cell Lymphoma, Other Most cases of primary cutaneous DLBCLs are either follicle center with diffuse/large cell transformed type, or of the leg type. 42 However, the other category consists of rarer lesions that can be subcategorized into well-known morphologic entities: T-cell/histiocyte-rich large B-cell lymphoma (TC/HR LBCL), plasmablastic lymphoma, and intravascular lymphoma. The TC/HR LBCL of the skin has a better prognosis compared to its nodal/noncutaneous counterparts. Complete clinical staging is of paramount importance, to distinguish between primary cutaneous and systemic disease. Precursor Hematologic Neoplasms Blastic Plasmacytoid Dendritic Cell Neoplasm. This new addition to the WHO-EORTC classification scheme is defined by immunohistochemical expression of CD4 and CD This lesion used to be known as blastic NK-cell lymphoma and CD4 þ /CD56 þ hematodermic neoplasm. The neoplastic cells express CD4, CD43, and CD56. In addition, the plasmacytoid dendritic cell associated antigens CD123 Arch Pathol Lab Med Vol 139, March 2015 IHC in Cutaneous Lymphoma Dewar et al 347

11 Figure 8. Pseudoclonality in a TRG assay. The initial polymerase chain reaction amplification (top) demonstrates a dominant peak, consistent with a T-cell clone. On repeated testing (bottom), however, the specimen shows 3 peaks, consistent with an oligoclonal proliferation. (interleukin 3a chain receptor), BDCA-2/CD303, TCL1, and CLA, and the interferon a dependent molecule MxA, are also expressed. CD4, CD56, CD43, and CD123 are commonly used immunostains. USE OF CLONALITY STUDIES IN THE DIAGNOSIS OF PRIMARY CUTANEOUS LYMPHOMA Both T- and B-cell clonality studies form an essential ancillary test 55 in diagnosis of cutaneous lymphoma for the following reasons: many of the primary cutaneous lymphomas do not have or fail to demonstrate antigenic aberrancies, compared to their nodal or extracutaneous counterparts. Exuberant cutaneous B-cell hyperplasia can mimic cutaneous lymphoma (marginal zone lymphoma), and demonstrating clonality is essential to support a diagnosis of lymphoma. Both B- and T-cell clonality studies, as done currently by using BIOMED-II validated primers against targets such as IGH, IGK, IGL, TRG, and TRB, have several rounds of redundancies and hence are sensitive for capturing most of the cutaneous lymphomas (up to 90%). Two important caveats should be remembered when ordering antigen receptor gene rearrangement studies for cutaneous lymphoid lesions. One, gene rearrangement studies are never a substitute for a thorough morphologic and immunophenotypic evaluation. In fact, clonality studies should be emphasized as valuable ancillary studies and should always be interpreted in conjunction with clinical, morphologic, and immunohistochemical data. In those cases where clinical and morphologic features were suggesting a benign lesion and a gene rearrangement study result is positive, a note indicating this discrepancy should be added to the diagnosis. Watchful waiting and clinical follow-up may be indicated in many cases, instead of reclassifying the lesion as a lymphoma solely on the basis of positive clonality study findings alone. A direct conversation with a clinician is appropriate in these circumstances, which may lead to reevaluation of the clinical findings. This is particularly true in the interpretation of TCR clonality studies, which may have a high degree of positivity based on interpretative thresholds and techniques (primer sets) used. The TCR gene rearrangement studies can be positive in benign inflammatory diseases too, but when multiplex polymerase chain reaction primers are used, the falsepositive rate is typically low (2.3% in one series). 56 Secondly, antigen receptor gene rearrangement studies should never be used as a surrogate to make a definitive diagnosis when biopsied tissue is limited and should probably not be ordered in the absence of a lymphoid infiltrate. Smaller lymphoid infiltrates, especially a partially sectioned (focal) germinal center, may result in pseudoclonal patterns in electropherograms, owing to limited IGH repertoire amplification or an interpretation bias due to the lack of a good Gaussian distribution of reactive lymphocytes in the background. When only a very limited number of B or T cells are present in the sample, these studies may selectively amplify a single cell that might simulate a clone. 57,58 Thus, when sample is limited, instead of requesting gene rearrangement studies, a repeated biopsy is often of better yield to establish an accurate diagnosis. Because skin biopsies are inherently small, which can result in the abovementioned artifacts, all gene rearrangement studies in this setting should be viewed cautiously owing to the possibility of false-positive results. To reduce false-positive results due to selective amplification in a truly reactive process, repeated studies should be performed on the same sample and the clonal population should be of identical size on the electropherograms (Figure 8). Oligoclonality or false clonality will not usually be reproducible and the finding of the same clone from different amplifications is often reassuring. Even more helpful is testing of samples from more than 1 site. Several studies have demonstrated that detecting the same clone from different sites, including a single skin and peripheral blood sample, increases the reliability of these tests. Therefore, when results are questionable, one can request retesting on a new sample for comparison of the possible clone. In T-cell 348 Arch Pathol Lab Med Vol 139, March 2015 IHC in Cutaneous Lymphoma Dewar et al

12 proliferations, the combined detection of both TRG and TRB rearrangements has been shown to increase the reliability of detection of a true clone, but this approach will underdiagnose clonality in some cases. 62 Although the BIOMED-II primers have greatly improved our ability to detect B- and T-cell clones in paraffinembedded tissues, false-negative results may still occur. 63,64 These may be secondary to DNA degradation due to formalin fixation or due to the inability of the primers used in the test to actually anneal with the clonal rearrangement. Therefore, in the presence of morphologic and immunophenotypic evidence of lymphoma, a negative antigen receptor gene rearrangement study finding should not be interpreted as evidence of a benign proliferation. TARGETED THERAPIES AND IHC Many monoclonal antibody therapies are available either as primary or secondary regimen in the treatment of cutaneous lymphoma; some clinical trials are in progress to establish the efficacies in these disorders, particularly in the areas of late-stage MF, CD30 þ anaplastic large cell lymphoma, or most low-grade and high-grade B-cell lymphomas. If treatment with a monoclonal antibody is being considered, it is appropriate that IHC be performed to demonstrate the presence of target antigen (especially for CD20 and CD30) and that IHC be done at follow-up to show efficacy of treatment. Examples of such targeted therapies include rituximab, alemtuzumab targeting CD52, 34 and brentuximab targeting CD30 (Ber-H2). 22,26 The pathologist should be aware that there are no consensus guidelines in the interpretation of these results following therapy and that presence or absence of the marker may correlate poorly with response to therapy. SUMMARY The above framework of cutaneous lymphoid lesions based on the WHO-EORTC classification is not complete. This review provides pertinent challenges, focused on the most challenging entities as well as newer entities. As many of these provisional entities evolve, with better-defined markers along with newer techniques such as genomics, it is expected that many of these entities will be further refined for practical diagnosis. In addition, the availability of targeted therapy may make a theranostic classification of these disorders more practical and useful than a pure morphologic or phenotype-based classification in the future. References 1. Willemze R, Meijer CJ. Classification of cutaneous T-cell lymphoma: from Alibert to WHO-EORTC. J Cutan Pathol. 2006;33(suppl 1): Willemze R, Kerl H, Sterry W, et al. EORTC classification for primary cutaneous lymphomas: a proposal from the Cutaneous Lymphoma Study Group of the European Organization for Research and Treatment of Cancer. Blood. 1997;90(1): Jaffe ES, Harris NL, Stein H, Vardiman JW, eds. Pathology and Genetics of Tumours of the Haematopoietic and Lymphoid Tissues. Lyon, France: IARC Press World Health Organization Classification of Tumours; vol Willemze R, Jaffe ES, Burg G, et al. WHO-EORTC classification for cutaneous lymphomas. Blood. 2005;105(10): Swerdlow SH, Campo E, Harris NL, et al, eds. WHO Classification of Tumours of Haematopoietic and Lymphoid Tissues. Lyon, France: IARC Press World Health Organization Classification of Tumours; vol Fung MA, Murphy MJ, Hoss DM, Grant-Kels JM. Practical evaluation and management of cutaneous lymphoma [quiz in J Am Acad Dermatol. 2002;46(3): ] J Am Acad Dermatol. 2002;46(3): Hedrich CM, Rauen T, Crispin JC, et al. camp-responsive element modulator alpha (CREMa) trans-represses the transmembrane glycoprotein CD8 and contributes to the generation of CD3þCD4-CD8- T cells in health and disease. J Biol Chem. 2013;288(44): Neidhart M, Fehr K, Pataki F, Michel BA. The levels of memory (CD45RA-, ROþ) CD4þ and CD8þ peripheral blood T-lymphocytes correlate with IgM rheumatoid factors in rheumatoid arthritis. Rheumatol Int. 1996;15(5): Krajewski AS, Myskow MW, Salter DM, Cunningham DS, Ramage EF. Diagnosis of T-cell lymphoma using beta F1, anti-t-cell receptor beta chain antibody. Histopathology. 1989;15(3): Quintanilla-Martinez L, Jansen PM, Kinney MC, Swerdlow SH, Willemze R. Non-mycosis fungoides cutaneous T-cell lymphomas: report of the 2011 Society for Hematopathology/European Association for Haematopathology workshop. Am J Clin Pathol. 2013;139(4): Roullet M, Gheith SM, Mauger J, Junkins-Hopkins JM, Choi JK. Percentage of {gamma}{delta} T cells in panniculitis by paraffin immunohistochemical analysis. Am J Clin Pathol. 2009;131(6): Rodriguez-Pinilla SM, Ortiz-Romero PL, Monsalvez V, et al. TCR-gamma expression in primary cutaneous T-cell lymphomas. Am J Surg Pathol. 2013; 37(3): Song SX, Willemze R, Swerdlow SH, Kinney MC, Said JW. Mycosis fungoides: report of the 2011 Society for Hematopathology/European Association for Haematopathology workshop. Am J Clin Pathol. 2012;139(4): Izban KF, Hsi ED, Alkan S. Immunohistochemical analysis of mycosis fungoides on paraffin-embedded tissue sections. Mod Pathol. 1998;11(10): Stevens SR, Ke MS, Birol A, et al. A simple clinical scoring system to improve the sensitivity and standardization of the diagnosis of mycosis fungoides type cutaneous T-cell lymphoma: logistic regression of clinical and laboratory data. Br J Dermatol. 2003;149(3): Kempf W, Kazakov DV, Cipolat C, Kutzner H, Roncador G, Tomasini D. CD4/CD8 double negative mycosis fungoides with PD-1 (CD279) expression a disease of follicular helper T-cells? Am J Dermatopathol. 2012;34(7): Tournier E, Laurent C, Thomas M, et al. Double-positive CD4/CD8 mycosis fungoides: a rarely reported immunohistochemical profile. J Cutan Pathol. 2013; 41(1): Ishida M, Hotta M, Takikita-Suzuki M, Kojima F, Okabe H. CD8-positive granulomatous mycosis fungoides: a case report with review of the literature. J Cutan Pathol. 2010;37(10): Furlan FC, de Paula Pereira BA, da Silva LF, Sanches JA. Loss of melanocytes in hypopigmented mycosis fungoides: a study of 18 patients. J Cutan Pathol. 2013;41(2): Yao X, Teruya-Feldstein J, Raffeld M, Sorbara L, Jaffe ES. Peripheral T-cell lymphoma with aberrant expression of CD79a and CD20: a diagnostic pitfall. Mod Pathol. 2001;14(2): Benner MF, Jansen PM, Vermeer MH, Willemze R. Prognostic factors in transformed mycosis fungoides: a retrospective analysis of 100 cases. Blood. 2012;119(7): Olsen EA, Whittaker S, Kim YH, et al. Clinical end points and response criteria in mycosis fungoides and Sezary syndrome: a consensus statement of the International Society for Cutaneous Lymphomas, the United States Cutaneous Lymphoma Consortium, and the Cutaneous Lymphoma Task Force of the European Organisation for Research and Treatment of Cancer. J Clin Oncol. 2011;29(18): Kelemen K, Guitart J, Kuzel TM, Goolsby CL, Peterson LC. The usefulness of CD26 in flow cytometric analysis of peripheral blood in Sezary syndrome. Am J Clin Pathol. 2008;129(1): Meyerson HJ, Awadallah A, Pavlidakey P, Cooper K, Honda K, Miedler J. Follicular center helper T-cell (TFH) marker positive mycosis fungoides/sezary syndrome. Mod Pathol. 2013;26(1): O Malley DP, Chizhevsky V, Grimm KE, Hii A, Weiss LM. Utility of BCL2, PD1, and CD25 immunohistochemical expression in the diagnosis of T-cell lymphomas. Appl Immunohistochem Mol Morphol. 2014;22(2): Kempf W, Pfaltz K, Vermeer MH, et al. EORTC, ISCL, and USCLC consensus recommendations for the treatment of primary cutaneous CD30- positive lymphoproliferative disorders: lymphomatoid papulosis and primary cutaneous anaplastic large-cell lymphoma. Blood. 2011(15);118: Kempf W. CD30þ lymphoproliferative disorders: histopathology, differential diagnosis, new variants, and simulators. J Cutan Pathol. 2006;33(suppl 1): Greisser J, Palmedo G, Sander C, et al. Detection of clonal rearrangement of T-cell receptor genes in the diagnosis of primary cutaneous CD30 lymphoproliferative disorders. J Cutan Pathol. 2006;33(11): Guitart J, Querfeld C. Cutaneous CD30 lymphoproliferative disorders and similar conditions: a clinical and pathologic prospective on a complex issue. Semin Diagn Pathol. 2009;26(3): Jhala DN, Medeiros LJ, Lopez-Terrada D, Jhala NC, Krishnan B, Shahab I. Neutrophil-rich anaplastic large cell lymphoma of T-cell lineage: a report of two cases arising in HIV-positive patients. Am J Clin Pathol. 2000;114(3): Salama S. Primary cutaneous T-cell anaplastic large cell lymphoma, CD30þ, neutrophil-rich variant with subcutaneous panniculitic lesions, in a postrenal transplant patient: report of unusual case and literature review. Am J Dermatopathol. 2005;27(3): Cardoso J, Duhra P, Thway Y, Calonje E. Lymphomatoid papulosis type D: a newly described variant easily confused with cutaneous aggressive CD8-positive cytotoxic T-cell lymphoma. Am J Dermatopathol. 2012;34(7): Plaza JA, Feldman AL, Magro C. Cutaneous CD30-positive lymphoproliferative disorders with CD8 expression: a clinicopathologic study of 21 cases. J Cutan Pathol. 2013;40(2): Arch Pathol Lab Med Vol 139, March 2015 IHC in Cutaneous Lymphoma Dewar et al 349