Difficulties in the diagnosis of spitzoid melanocytic lesions

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1 For reprint orders, please contact Difficulties in the diagnosis of spitzoid melanocytic lesions Expert Rev. Dermatol. 5(5), (2010) Stephen H Olsen 1, Rajiv M Patel 1, Linglei Ma 1 and Douglas R Fullen 1 1 Dermatopathology Section, Department of Pathology, University of Michigan, M3261, Medical Sciences I, 1301 Catherine, Ann Arbor, MI , USA Author for correspondence: Tel.: Fax: dfullen@med.umich.edu Spitz nevus was first described in 1948 by Dr Sophie Spitz, who termed it juvenile melanoma based on its striking cytologic resemblance to melanoma, being composed of large epithelioid and spindle cells, and its prevalence among children. Several changes in terminology have since occurred with increased knowledge and experience, particularly regarding its occurrence in adult populations and rather indolent clinical behavior. Nevertheless, the distinction of Spitz nevus from melanoma still remains a significant problem in dermatopathology. Most classic examples of Spitz nevi can be easily distinguished histopathologically from melanoma, although lesions with unusual or atypical features still pose diagnostic difficulties, particularly in small or partial samples. In general, poor interobserver diagnostic concordance is not uncommon. Herein, we review the histopathological features of Spitz nevi, including common and recently reported variants, and spitzoid melanoma, and discuss recent advances in ancillary studies that may prove useful in their diagnosis. Keywords: atypical Spitz tumor Spitz nevus spitzoid melanoma Medscape: Continuing Medical Education Online This activity has been planned and implemented in accordance with the Essential Areas and policies of the Accreditation Council for Continuing Medical Education through the joint sponsorship of Medscape, LLC and Expert s Ltd. Medscape, LLC is accredited by the AC to provide continuing medical education for physicians. Medscape, LLC designates this educational activity for a maximum of 1.0 AMA PRA Category 1 Credits. Physicians should only claim credit commensurate with the extent of their participation in the activity. All other clinicians completing this activity will be issued a certificate of participation. To participate in this journal activity: (1) review the learning objectives and author disclosures; (2) study the education content; (3) take the post-test and/or complete the evaluation at (4) view/print certificate. Learning objectives Upon completion of this activity, participants should be able to: Describe clinical features and classification of Spitz nevi. Describe histopathologic features distinguishing Spitz nevi from atypical Spitz tumor and spitzoid melanoma. Describe immunohistochemistry and other ancillary studies that may help differentiate these three lesion types. Financial & competing interests disclosure Editor Elisa Manzotti, Editorial Director, Future Science Group, London, UK Disclosure: Elisa Manzotti has disclosed no relevant financial relationships. Author Laurie Barclay, MD, Freelance writer and reviewer, Medscape, LLC Disclosure: Laurie Barclay has disclosed no relevant financial relationships. Authors Stephen H Olsen, MD, Dermatopathology Section, Department of Pathology, University of Michigan, MI, USA Disclosure: Stephen H Olsen has disclosed no relevant financial relationships. Rajiv M Patel, MD, Dermatopathology Section, Department of Pathology, University of Michigan, MI, USA Disclosure: Rajiv M Patel has disclosed no relevant financial relationships. Linglei Ma, MD, PhD, Dermatopathology Section, Department of Pathology, University of Michigan, MI, USA Disclosure: Linglei Ma has disclosed no relevant financial relationships. Douglas R Fullen, MD, Dermatopathology Section, Department of Pathology, University of Michigan, MI, USA Disclosure: Douglas R Fullen has disclosed no relevant financial relationships /EDM Expert s Ltd ISSN

2 Olsen, Patel, Ma & Fullen Classic Spitz nevus & variants Classic Spitz nevus Spitzoid lesions are composed of varying proportions of spindled and epithelioid cells that display a characteristic cytomorphology that is the common thread between the classic Spitz nevus and all its variants [1]. The cells are large, contain abundant eosinophilic to amphophilic cytoplasm, and have nuclei with smooth nuclear membranes, delicate chromatin and prominent central nucleoli. Within a given lesion, spitzoid cells are generally uniform in size and appearance. Classic Spitz nevi can be compound (most common), junctional or intradermal (Figure 1) [2]. Although originally thought to arise in children, patients older than 20 years may account for up to 66% of cases, and these patients are predominantly female [3]. As with other benign nevi, Spitz nevi are symmetrical from side to side, but typically have a wedge-shaped silhouette when compound or intradermal. They are generally sharply circumscribed that is, lesions with junctional components terminate as nests on each side. There are associated epidermal changes, ranging from mild acanthosis to pseudoepitheliomatous hyperplasia, which are more prominent in lesions with junctional components. Kamino bodies, or globular collections of eosinophilic (periodic acid-schiffpositive) basement membrane material, are often present. Nevus cells are distributed mostly in nests along the dermal epidermal junction with only minor components of single units, except in occasional examples of early or evolving junctional Spitz nevi. Nests often exhibit artifactual peripheral clefting from the surrounding epidermis. When spindled, cells within junctional nests can be oriented perpendicular to the surface, thereby appearing to rain down. Nests can extend into the upper levels of the epidermis, a phenomenon referred to as transepidermal elimination. Single cells, if present, tend to remain low within the epidermis, lack pagetoid scatter, and are confined to the center of the lesion. Dermal nevus cells are nested superficially and most exhibit maturation, characterized by diminution in cell size and dispersion from nests between collagen bundles, with deeper descent into the dermis. Moreover, the dermal component does not distort the normal dermal architecture. Mitotic activity can be found in some lesions; however, it is usually sparse, when present, and Figure 1. Conventional Spitz nevus. (A) Low power circumscription and symmetry with epidermal hyperplasia (40 ). (B) Nests of epithelioid melanocytes are arranged vertically to the skin surface with raining down appearance (100 ). (C) Higher magnification shows epithelioid melanocytes, Kamino body and occasional pagetoid scattering (200 ). limited to the spitzoid cells of the junctional and superficial dermal components. Pigment is generally absent, but cells can demonstrate light dusty pigmentation occasionally. Inflammation is seen in approximately 70% of lesions and when heavy, the findings are consistent with a halo Spitz nevus. Multinucleated melanocytes are present in 25% of Spitz nevi and are seen more often in adults [3] and in nevi with epithelioid morphology [2]. Pigmented spindle cell nevus Many dermatopathologists believe the pigmented spindle cell nevus (PSCN) of Reed, or Reed s nevus, represents one end of the spectrum of Spitz nevi, composed exclusively of spindled cells with the aforementioned spitzoid cytomorphology. These lesions tend to be junctional (Figure 2) [2]. Like classic Spitz nevi, individual PSCN lesions are sharply circumscribed, associated with epidermal hyperplasia, and form flat-topped, heavily pigmented papules. The cells form moderate-to-large-sized nests along the dermal epidermal junction. Within these nests, spindle cells can be arranged in a vertically oriented or raining down fashion, a whirling pattern, or less commonly oriented parallel to the epidermal surface. Copious amounts of granular melanin pigment are present within the cytoplasm of nevus cells, as well as in adjacent keratinocytes. Pigment is also present within the parakeratotic scale of the stratum corneum and within dermal melanophages. These lesions must be distinguished from melanoma in situ. While this is usually easily accomplished, it may be a challenge in partially sampled lesions, or those with superimposed features of irritation. When a PSCN is compound, the dermal component is often cellular, fills the papillary dermis and has a broad and pushing border along the base of the lesion. Desmoplastic Spitz nevus Desmoplastic Spitz nevi reside on the opposite end of the spectrum from PSCN (Reed s nevus), being composed mostly of epithelioid cells (Figure 3). They most often occur on the extremities of adults, predominantly females, in their third decade [4]. Lesions are most commonly intradermal, but may rarely be compound, albeit with minor junctional components. From scanning magnification, these lesions are usually symmetrical, circumscribed and wedge-shaped, with the apex of the lesion pointing into the mid- or deep-dermis. Epidermal hyperplasia is not pronounced, and Kamino bodies are not a typical feature. The cells in the dermis may cluster and form small nests superficially, but often are arrayed as single cells and cords. They are set, at least partially, within a sclerotic dermal stroma consisting of thickened and hyalinized collagen bundles that may resemble keloidal collagen. As with classic Spitz nevi, the cells exhibit some histologic evidence of maturation with descent into the dermis. Mitotic activity, when present, is rare and limited to the upper dermis. The differential diagnosis rests mainly 550 Expert Rev. Dermatol. 5(5), (2010)

3 Difficulties in the diagnosis of spitzoid melanocytic lesions and circumscription, lack of a significant junctional component in most cases, more uniform cytomorph ology of the spitzoid cells, and maturation of the spitzoid cells as they descend in the dermis for the latter. Vascular and fibro h istiocytic lesions can be differentiated from angiomatoid Spitz nevus by evaluation of appropriate immunohistochemical stains. Figure 2. Pigmented spindle cell nevus. (A) Circumscribed and symmetric lesion (40 ). (B) Mostly junctional nevus composed of heavily pigmented spindled melanocytes (100 ). (C) Heavily pigmented and spindled melanocytes without cytologic atypia (200 ). with desmoplastic melanoma. Desmoplastic melanoma has an infiltrative growth pattern (in contrast to the wedge-shaped and symmetrical growth of a desmoplastic Spitz nevus), patchy dermal inflammation and often an atypical junctional melanocytic proliferation overlying the invasive melanoma from low magnification. The melanoma cells have cytologic atypia, are often predominantly spindled and lack spitzoid cytomorphology. Spitzoid dysplastic (Spark s) nevus The Spark s nevus (melanocytic nevus with features of Spitz and Clark s/dysplastic nevus) combines cytomorphologic features of Spitz nevi with the altered architectural patterning commonly associated with Clark s dysplastic nevi (Figure 5). In practice, they can be referred to by the more descriptive term spitzoid dysplastic nevi. In a series reported by Ko et al., these lesions occurred in adults, mostly female, and were most commonly located on the trunk and lower extremities [6]. Spitzoid dysplastic nevi are either junctional or compound, and are composed of variable proportions of spindled and epithelioid spitzoid-appearing melanocytes. Angiomatoid Spitz nevus The angiomatoid Spitz nevus is a rare lesion thought to be a variant of desmoplastic Spitz nevus [5]. Similarly, the angio matoid variant occurs in adults, most commonly females in their third decade, on the extremities. Lesions are symmetrical and circumscribed, and are predominantly intradermal processes, although a minor junctional component can be found occasionally. Most lesions are composed of epithelioid cells disposed singly or in small clusters, set within a dense fibrous stroma (F igure 4). These epithelioid melanocytes can be rare and difficult to observe in some lesions. Mitotic activity is rare and, when present, limited to the superficial dermis. A variable but often prominent number of slightly thick-walled blood vessels are embedded within the desmoplastic stroma and accompanied by a variably dense lymphocyte-predominant inflammatory host response that may or may not contain plasma cells. The pattern of the inflammatory infiltrate is usually perivascular, but can be diffuse. The significance of this variant is in its differential diagnosis with partially regressed or desmoplastic melanoma, but it must also be distinguished from a vascular lesion and epithelioid fibrous histiocytoma. Regressed melanoma can usually be distinguished from angiomatoid Spitz nevus by the smaller size Figure 3. Desmoplastic Spitz nevus. (A) Dermal-based lesion (40 ). (B & C) Spindled and epithelioid melanocytes are arranged as fascicles or single units between sclerotic collagen bundles (100 and 200, respectively). (D) Sclerotic collagen and epithelioid/spindled melanocytes (400 ). 551

4 Olsen, Patel, Ma & Fullen potential for malignant degeneration of spitzoid dysplastic nevi and underscores the importance of distinguishing them from melanoma and achieving complete excision of these lesions. If only a portion of the lesion is present for interpretation in the initial biopsy, and diagnostic uncertainty exists as to whether the lesion is a spitzoid dysplastic nevus or melanoma, then it is advisable to issue a provisional diagnosis with a differential diagnosis that includes melanoma and recommend complete excision for complete histologic examination. Atypical Spitz tumor The atypical Spitz tumor (AST) is a term designated for borderline lesions and, in practice, conveys a degree of uncertainty or unpredictability regarding the biologic behavior of an individual lesion. Clinical and particularly histologic features deviate significantly from those attributed to the classic Spitz nevus and can overlap with those of melanoma [8]. However, the vast majority of patients, particularly those who are prepubertal, have behaved in a clinically indolent fashion [9]. Atypical Spitz tumors are usually compound lesions composed predominantly Figure 4. Angiomatoid Spitz nevus. (A) Dermal-based lesion (40 ). (B & C) Spindled of epithelioid cells. While there may be and epithelioid melanocytes are set in a dense fibrous stroma, associated with prominent blood vessels (100 and 200, respectively). (D) Epithelioid/spindled melanocytes and histologic features of Spitz nevus, lesions prominent vessels (400 ). tend to be larger, asymmetric and not as circumscribed as classic Spitz nevus. They The spitzoid melanocytes are disposed in regularly sized nests demonstrate cytologic atypia, including nuclear pleomorphism, irregularly on the sides and tips of often hyperplastic rete ridges and aberrant sheet-like growth resulting from a dense, comalong the dermal epidermal junction, with extensive bridging of pact cellularity that distorts the dermal architecture (Figure 6). nests between rete ridges in a horizontal or plaque-like pattern. Maturation with dermal descent is lacking and mitotic activity is The junctional component extends laterally or shoulders beyond often present, including in the deep dermis. Cerroni et al. recently the dermal component in compound lesions. Foci of small clus- found the presence of mitoses, and mitoses near the base of the ters and single-unit melanocytes can be found in the epidermis lesion to be significant features in distinguishing lesions with primarily within the center of the lesion. Variable numbers of unfavorable clinical behavior from those with favorable behavkamino bodies can also be seen in the epidermis. Fibroplasia is ior, corroborating previous reports [8,10 12]. Other findings that present in the papillary dermis, although less commonly in lesions can be seen include ulceration, extension into the deep dermis or containing more epithelioid cells. In compound spitzoid dysplas- upper subcutis, and a bulbous or expansile and pushing border tic nevi, the dermal component is usually small and limited to at the base of the lesion. While many of these histologic features the papillary dermis. Maturation of the dermal component with can be seen in melanoma, they are often present in conjuncdeeper descent into the dermis is common. Mitotic activity is rare. tion with other conventionally reassuring criteria, making these In contrast to melanoma, spitzoid dysplastic nevi generally lack lesions exceedingly difficult to classify with certainty. This issue is significant melanocyte involvement of suprapapillary plates and, underscored by the well-documented low diagnostic concordance therefore, junctional confluence or pagetoid scatter. Moreover, among expert dermatopathologists in classifying these lesions as spitzoid dysplastic nevi are symmetrical, laterally circumscribed benign or malignant [10,13]. Pertinent histopathologic findings and typically smaller lesions than superficial spreading melanoma. of Spitz nevus, AST and spitzoid melanoma are summarized in However, similar lesions with high-grade cytologic atypia, pleomor- Table 1. Due to the ambiguous nature of this diagnosis, patients phism and pagetoid scattering have been described in contiguity are often treated as for melanoma, with sentinel lymph node biopwith superficial spreading melanoma [7]. This finding suggests a sies (SLNB) undertaken for lesions deeper than 1 mm. Multiple 552 Expert Rev. Dermatol. 5(5), (2010)

5 Difficulties in the diagnosis of spitzoid melanocytic lesions reports show a relatively high proportion of positive sentinel lymph nodes (SLNs), up to 40 50%. In the past, the presence of any atypical cells in SLNs in this setting was taken as evidence of aggressive behavior and the primary skin lesions were retrospectively classified as melanoma. However, as multiple series demonstrate, the vast majority of these lesions do not show a similar aggressive behavior to conventional melanoma [9,14 16]. The pattern of lymph node involvement, tumor burden and presence of mitotic activity are important features to identify when evaluating melanocytic deposits in this setting. In general, lymph node deposits within the parenchyma and large size of a deposit that effaces the nodal architecture are adverse features. Furthermore, characterization by molecular methods, such as comparative genomic hybridization (CGH) or FISH, may give additional information to help guide therapy (see later). Spitzoid melanoma Figure 5. Spitzoid dysplastic nevus. (A) Small and circumscribed lesion (20 ). Spitzoid melanoma can arise de novo or (B & C) Epidermal hyperplasia and bridging of junctional nests (40 and 100, within a pre-existing nevus [17] ; thus, fearespectively). (D) Horizontal bridging of junctional nests with concentric fibroplasia and mild tures of a Spitz nevus or its variants can be dermal inflammation. The melanocytes are epithelioid. Kamino bodies are present (200 ). present in the background of a melanoma and confound the diagnosis. The junctional component may be invasion. Although spitzoid melanoma in children may have a nested, although nests are larger and more irregular and predomi- better prognosis than in adults, some young patients still develop nated in areas by single-unit melanocytes with pagetoid scattering. metastases and die from the disease [18]. Spitzoid melanomas are more often associated with epidermal atrophy, resulting from consumption of the epidermis, rather than Ancillary studies the hyperplasia commonly seen in Spitz nevi (Figure 7). There may Although careful evaluation of hematoxylin and eosin-stained be clefting around nests, as is observed in Spitz nevi, but dysco sections remains the gold standard for the diagnosis of spitzoid hesion of melanocytes within nests is more characteristic of spitzoid lesions, ancillary studies have become increasingly important, melanoma. Kamino bodies can also be seen, but they are scarce particularly when the pathologist is faced with a limited specimen, and not well formed when compared with Spitz nevi. Ulceration such as a partial punch or superficial shave biopsy. may be present and is more common in melanoma. The invasive dermal component demonstrates similar features to those listed Immunohistochemistry for AST. It can form large nodules of compact, sheet-like growth, Many markers have been proposed as useful for distinguishing resulting from high cellularity, which may compress or disrupt spitzoid lesions from conventional nevi and melanoma. Common surrounding structures of the dermis. The cells exhibit cytologic and recent promising markers are reviewed later. atypia, which is often high grade, and includes prominent nuclear Spitz nevi and melanoma show diffuse immunoreactivity for pleomorphism. There is no maturation of the spitzoid melano- S-100 protein and Melan-A. Studies of HMB-45 and Ki-67 cytes with descent into the dermis. Mitotic activity is conspicuous, (MIB-1) in spitzoid lesions have yielded varying results, with including in deep aspects of the lesion, features recently found to some groups finding these stains useful and others finding be significantly associated with unfavorable clinical behavior [10]. them not useful. Bergman and colleagues reported that Spitz In fact, some authors believe that more than six mitoses per mm 2 nevi demonstrate a stratification pattern of HMB-45 stainor three mitoses per high power field are concerning for or favor ing manifested as decreasing immunoreactivity as the lesional melanoma [8,17]. An inflammatory host response often presents as cells progress from the junction and superficial dermis to the a banded infiltrate of lymphocytes and plasma cells, which can be base of the lesion [19]. By contrast, spitzoid melanomas tend to associated with regression and melanosis. More adverse diagnostic have greater HMB-45 expression in the deep dermal component features include necrosis, angiolymphatic spread and perineural than Spitz nevi. Others have asserted that classic Spitz nevi have 553

6 Olsen, Patel, Ma & Fullen useful than a Ki-67 index in inflamed spitzoid lesions [17]. We have found HMB-45 and Ki-67 immunohistochemistry helpful in a subset of cases. S100A6, a member of the S100 protein family of calcium-binding proteins, has shown promise for differentiating between Spitz nevi, melanomas and melanocytic nevi. Ribe and colleagues recently reported strong diffuse cytoplasmic staining in both the junctional and dermal components of 100% of analyzed Spitz nevi. By contrast, only 33% of melanomas demonstrated S100A6 expression, mainly in a weak or patchy pattern in the dermal component, with absent or minimal immunostaining in the junctional component. Moreover, 56% of different melanocytic nevi expressed this marker, nearly all of them weakly and in the dermal component only. The authors concluded that S100A6 could be used to distinguish Spitz nevi from melanoma in classic cases and in cases difficult to distinguish by light microscopy [22]. Differentiating desmoplastic Spitz nevi from desmoplastic melanoma may be difficult, particularly when faced with a limited biopsy and incomplete clinical information. Loss of the CDKN2a gene Figure 6. Atypical Spitz tumor. (A) Dermal-based lesion with sheet-like growth product p16 is thought to be involved in pattern and incomplete maturation (40 ). (B & C) Nests do not become smaller in melanomagenesis via dysregulation of the deeper dermis (100 and 200, respectively). (D) Melanocytes are epithelioid with nuclear pleomorphism (400 ). cell cycle and is indicative of a poorer prognosis in patients with melanoma. Hilliard a more heterogeneous staining pattern [20]. Although there is and colleagues recently reported loss or weak expression of p16 some debate, increased immunoreactivity for HMB-45 in the in 81.8 and 18.2%, respectively, of desmoplastic melanomas by deep portions of a lesion, in conjunction with ambiguous or immunohistochemistry. All desmoplastic Spitz nevi studied were worrisome clinical and histo pathologic findings, may be help- moderately or strongly immunoreactive for p16. In the authors ful in distinguishing spitzoid melanoma from compound Spitz experience, the p16 pattern, in conjunction with S100 staining, nevi [19]. The utility of HMB-45 stratification for distinguishing the Ki-67 index and clinical and histologic features, was useful in between Spitz nevi and AST has not been well-characterized. distinguishing between desmoplastic melanoma and desmoplastic Pure desmoplastic melanoma is generally, although not always, Spitz nevus [23]. negative for markers other than S100, and, therefore, positivity for Melan-A and HMB-45 could help to distinguish it from Molecular studies desmoplastic Spitz nevus. Melanoma typically contains complex genotypic abnormalities, Measurement of the mitotic rate in the dermal component of in contrast to Spitz nevi, which tend to have a normal karyotype spitzoid lesions is one of the most important factors in deter- when analyzed by CGH [24]. Some of the most exciting recent mining biologic potential [8]. Immunohistochemical labeling developments in the pathology of spitzoid lesions have been in the for Ki-67 (MIB-1) provides useful information beyond mitotic realm of molecular biology. Although these findings have by no count. A recent study demonstrated a Ki-67 proliferation index means been consistent between studies thus far, techniques such of 10% in ASTs relative to 0.53% for ordinary nevi, 5.04% in as CGH and FISH show promise as ancillary techniques for the conventional Spitz nevi and 36.83% in melanoma [21]. Caution diagnosis of ambiguous melanocytic lesions. must be exercised when interpreting this marker because Ki-67 immunoreactivity may be found in keratinocytes, mesenchymal BRAF/NRAS cells and inflammatory cells. As a result, direct evaluation of BRAF (v-raf murine sarcoma viral oncogene homolog B1) mutamitoses on hematoxylin and eosin-stained sections may be more tions may be found in approximately 50% of conventional 554 Expert Rev. Dermatol. 5(5), (2010)

7 Difficulties in the diagnosis of spitzoid melanocytic lesions Table 1. Pertinent histopathologic findings of Spitz nevus, atypical Spitz tumor and spitzoid melanoma. Feature Spitz nevus Atypical Spitz tumor Spitzoid melanoma Size <1 cm Often >1 cm >1 cm Symmetry Symmetric Often asymmetric Asymmetric Circumscription Sharply demarcated Variable, often not well circumscribed Ill-defined Ulceration Rare Variable, uncommon Common Cytologic atypia Uncommon Variably present Common Pleomorphism Uniform, monotonous Pleomorphic Pleomorphic Upward pagetoid spread Occasional, nests > single cells Common Common Kamino bodies Frequent Variable; may be poorly formed Less common; poorly formed Dermal cellularity Variable Prominent Prominent Sheet-like growth Absent Variable, common Common Expansile nodules Absent Variable, common Common Maturation Common Uncommon, variable Uncommon or absent Mitotic activity Uncommon, superficial Common, superficial and deep Common, superficial and deep melanomas and 80% of ordinary nevi [25,26], and a small subset of spitzoid melanomas [27]. The vast majority of conventional Spitz nevi do not contain BRAF mutations [26]. However, when the spectrum of spitzoid lesions is expanded to include unusual or atypical variants, such as spitzoid dysplastic nevi or Reed s nevi, the incidence of BRAF mutations is increased [27 29]. A limited number of studies have examined BRAF mutations in AST, and only one study reported finding a BRAF mutation in AST [25 27]. Mutations in NRAS (neuroblastoma RAS viral [v-ras] oncogene homolog) have also been reported in melanoma [25,26,28], but not in conventional Spitz nevi [25,26,28]. The inconsistencies between published studies may be related to a lack of consensus among dermatopathologists on histologic criteria used in the diagnosis of spitzoid melanocytic lesions [13]. Additional studies examining BRAF/NRAS mutations in a large series of well-characterized spitzoid melanocytic lesions with long-term follow-up are needed to clarify and expand on these findings. HRAS The majority of Spitz nevi have a normal karyotype. However, Bastian and colleagues recently used a combination of CGH and FISH to demonstrate amplification of chromosome 11p, corresponding to the location of HRAS (v-ha-ras Harvey rat sarcoma viral oncogene homolog), in a small subset of Spitz nevi [30]. Chromosome 11p copy number increases have also been noted in AST [25], but not in spitzoid melanoma [25,26]. Currently, there is no evidence to suggest that Spitz nevi with RAS activation are at risk for progression to melanoma. Further studies of spitzoid lesions with RAS activation are warranted to assess their biologic behavior [24]. CDKN2A Copy number loss of the cyclin-dependent kinase inhibitor 2A gene (CDKN2A) is frequently seen in melanoma, but not in conventional Spitz nevi. Takata and colleagues reported that three out of 16 ambiguous spitzoid lesions, most diagnosed as ASTs, had copy number loss of CDKN2A. A total of 12 unambiguous Spitz nevi lacked copy number loss of CDKN2A. The authors concluded that most ASTs show no evidence of genetic or epigenetic changes similar to conventional Spitz nevi, but a subset of ASTs may have genetic abnormalities, including copy number loss of CDKN2A [25]. TRPM1 mrna expression The transient receptor potential cation channel, subfamily M, member 1 (TRMP1/melanstatin-1/MLSN-1) expression has been shown to have prognostic value in primary cutaneous melanoma. Regional loss or complete absence of TRMP1 mrna was identified by Erickson and colleagues by in situ hybridization in 82% of melanomas, but only 1% of Spitz nevi. Of 16 patients with metastatic disease, 15 (94%) had primary tumors that demonstrated reduced MLSN-1 RNA expression by all or a portion of the dermal tumor [31]. The pattern of TRMP1 mrna expression may be helpful in differentiating Spitz nevi from melanoma, but additional studies are indicated. FISH Using existing data on DNA copy number alterations, Gerami and colleagues recently identified a panel of FISH probes applicable to paraffin-embedded tissue that were useful as an ancillary diagnostic tool in the diagnosis of melanoma. A combination of four probes targeting 6q23, 6p25, 6 centromere and 11q13, correctly classified melanoma with 86.7% sensitivity and 95.4% specificity when compared with various nevi, including Spitz nevi. Their study set also included 27 lesions with ambiguous morph ology, 24 of which were difficult to classify spitzoid lesions. Within this subset, their FISH probes identified six out of six lesions that later metastasized, although the details relating to the spitzoid cases are unclear. The authors suggested that a limited panel of FISH probes provided useful diagnostic information in 555

8 Olsen, Patel, Ma & Fullen of molecular abnormalities between different melanocytic lesions, the composition of probe sets for analyzing spitzoid lesions may prove to be different from those used in the ana lysis of conventional nevi and melanomas. CGH ana lysis of a large series and spectrum of spitzoid melanocytic lesions linked to clinical outcome may provide further insight into the molecular events that underpin these lesions and potentially form a rationale for identifying different FISH probes from those that are currently touted for distinguishing benign nevi from melanoma. Sentinel lymph node biopsy Unfortunately, little objective information on the frequency and biological implications of ectopic melanocytic cells in SLNB from patients with conventional Spitz nevi exists in the literature [36]. However, intracapsular nodal nevus cells have been found in staging lymphadenectomy specimens for epithelial malignancies in patients with and without a history of melanoma. Criteria for differentiating these deposits from melanoma have been previously proposed [37]. Based on proven prognostic benefit in melanoma, melanocytic deposits in an Figure 7. Spitzoid melanoma. (A) Expansile dermal tumor with surface ulceration extracapsular site within a SLN may lead (20 ). (B & C) Sheet-like growth pattern (40 and 100, respectively). (D) Epithelioid melanocytes with nuclear pleomorphism, prominent nucleoli and mitoses (400 ). surgeons to consider a completion lymphadenectomy in patients with ambiguous cases that could not be classified reliably by histopathology [32]. In spitzoid melanocytic lesions. Recent data suggest that this finding a more recent study, this group concluded that molecular abnor- does not have the same prognostic significance as in melanoma. malities in melanoma were heterogeneous and that the sensitiv- Ludgate and colleagues reported that 27 out of 57 patients (47%) ity of this probe set varied with the subtype of melanoma. This with atypical Spitz tumors had SLN involvement. All of these study included five difficult spitzoid lesions, four with benign and patients were alive and free of disease after a median follow-up of one with malignant clinical behavior on follow-up. Their FISH 43.8 months. These findings questioned the malignant potential ana lysis was positive in only one of their cases that had a benign of AST and the role of SLNB in their management. Interestingly, outcome [33]. Subsequently, Gaiser and colleagues, utilizing an however, one patient in this series who did not undergo SLNB identical FISH probe set, reported only a sensitivity of 60% and developed regional and distant metastases and died from metaspecificity of 50% in discriminating melanomas from nevi based static disease [9]. Busam and colleagues identified 11 individuals on a series of patients with histologically ambiguous lesions and of young age with atypical spitzoid melanocytic tumor (ASMT) long-term clinical follow-up. The authors concluded that this and positive SLN, and compared their clinical outcome to five probe set did not achieve sufficient sensitivity and specificity to be young patients with unequivocal melanoma and either a posiclinically useful in this setting [34]. Isaac and colleagues recently tive SLNB or death from disseminated disease. All patients reported polyploidy in four out of 41 benign Spitz nevi. Polyploidy with ASMT remained free of disease after a median follow-up was more common in agminate Spitz nevi and Spitz nevi with an of 47 months. This study confirmed prior observations suggestatypical epithelioid component [35]. ing that children and teenagers with ASMT and positive SLN FISH represents a promising ancillary diagnostic test for had a favorable prognosis, and again questioned the prognostic problem atic melanocytic lesions. However, results of recent value of SLNB in this clinical setting [16]. In a recent review of studies suggest that validation in larger series of patients with the literature on AST, approximately 17% of reported patients histologically well-characterized lesions and long-term follow-up with AST and positive SLN also had non-sln involvement. One is necessary before their use in routine diagnostic practice can patient had local recurrence, and all were alive and well after be recommended. Owing to differences in type and frequency 6 57 months follow-up [38]. The outcome of young patients with 556 Expert Rev. Dermatol. 5(5), (2010)

9 Difficulties in the diagnosis of spitzoid melanocytic lesions AST and positive lymph nodes is vastly superior to the overall 5-year survival of 68% seen in patients under the age of 19 years with regional metastatic melanoma [39]. Determining the ultimate role SLNB plays in the management of patients with ambiguous spitzoid lesions will likely require the outcome of randomized controlled trials of SLNB versus non-slnb in a large cohort of patients with long-term follow-up. Patients with unequivocal spitzoid melanoma should be managed clinically the same as other subtypes of melanoma, including consideration of a SLNB when the lesion is of sufficient Breslow depth [17]. Expert commentary Spitz nevi are uncommon nevi that can present with a variety of histologic appearances and can occur at any age, although they are most common in children, adolescents and young adults. The most common types of Spitz nevi include the classic spindled and epithelioid Spitz nevus, pigmented spindle cell nevus (Reed s nevus), spitzoid dysplastic or Spark s nevus, and desmoplastic Spitz nevus. The angiomatoid variant of Spitz nevus can be particularly difficult to diagnose. Spitz nevus may be admixed with other types of nevi to form a combined nevus. The cytomorphology of Spitz nevus cells, including the large size of spitzoid cells and the presence of macronucleoli, differs significantly from the nevomelanocytes of other common nevi and may present a challenge in distinguishing Spitz nevus from melanoma for a given lesion. Adding further to the diagnostic difficulty is that a small subset of melanomas has some histologic features that resemble Spitz nevi, but have sufficient criteria for malignancy and, therefore, are best classified as spitzoid melanomas. However, a small subset of spitzoid lesions, referred to by some authors as melanocytic tumor of uncertain malignant potential or atypical Spitz tumor, have histologic features that sufficiently deviate from the usual histology of Spitz nevi yet lack definitive criteria for malignancy, such that the biologic behavior of the lesions still cannot be reliably predicted on histologic grounds. SLNB has been performed for this type of lesion in many academic centers and has a surprisingly high rate of positivity, approaching 50% in some studies, although adverse outcomes are remarkably rare. There remains a lack of general consensus on the best diagnostic term to use for these lesions and the most appropriate treatment for these patients. We favor the term atypical Spitz tumor, for its specificity, over melanocytic tumor of uncertain malignant potential, which is a broader designation incorporating unrelated lesions, such as those in the blue nevus family. Ancillary studies, such as immunohistochemistry for MIB-1 proliferation index and HMB-45 staining pattern for presence or absence of stratification of the dermal component, have been used with variable results. Molecular ana lysis of pigmented lesions of the skin has become increasingly popular as an adjunct to histology and immunohistochemistry in defining the biologic behavior of an individual lesion. CGH has been applied to diagnostically challenging spitzoid lesions to look for gains or losses in genes commonly seen in melanoma as a means of guiding subsequent therapy. Recently, FISH has been developed with probes targeting 6q23, 6p25, 6 centromere and 11q13, and the assay has been reported to have a sensitivity of approximately 87% and an approximate 95% specificity. It remains unclear, however, whether this probe set is ideally suited for defining the biologic behavior in histologically ambiguous spitzoid lesions or their lymph node deposits. Five-year view The major emphasis in the diagnostic difficulty of Spitz nevi will continue to center around distinguishing Spitz nevi from spitzoid melanoma and defining whether the continued classification of a borderline category of atypical Spitz tumors is clinically justified. Outcome studies with longer follow-up will continue to elucidate the biologic behavior of these histologically ambiguous lesions and help guide the management of these patients. Molecular studies, such as CGH and targeted FISH, with results linked to patient outcomes, will be beneficial in stratifying the risk of a diagnostically challenging cutaneous lesion and determining whether SLNB is appropriate for an individual patient. Moreover, these studies should lead to defining the most appropriate areas of the genome to target in molecular assays to aid in prognosis, and the most appropriate treatment of these patients. Financial & competing interests disclosure The authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties. No writing assistance was utilized in the production of this manuscript. Key issues Spitz nevi and their variants are uncommon melanocytic lesions with characteristic morphology that differs significantly from that of common acquired nevi and can be mistaken for melanoma. Most Spitz nevi can be easily classified and distinguished from melanoma; however, diagnostic difficulty remains in a subset of lesions, particularly when faced with small and incomplete sampling. Atypical Spitz tumor is a lesion with overlapping features of Spitz nevus and spitzoid melanoma, which make it difficult to classify with certainty; many such lesions display indolent clinical behavior. Despite difficulties, histologic examination of hematoxylin and eosin-stained sections remains the gold standard for diagnosis, although ancillary studies have been investigated and may prove even more useful in the future. Molecular studies such as comparative genomic hybridization and FISH have shown promise, but additional work remains in specific application to histologically ambiguous spitzoid lesions

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