Spitzoid Melanoma Research Articles

Cutaneous melanoma: ESMO Clinical Practice Guidelines for diagnosis, treatment and follow-up†.

Cutaneous melanoma: ESMO Clinical Practice Guidelines for diagnosis, treatment and follow-up†.

1958P - A novel preclinical model of RAF-independent MEK1 mutant tumors and its treatment with novel ATP competitive MEK inhibitor

BackgroundA subgroup of MEK1 mutations in human tumors were recently described as RAF- and phosphorylation independent and as insensitive to currently clinically used allosteric MEK inhibitors. We established a novel cell line that carries a MEK1 mutation of this class (pGlu102_Lys104delinsGln) and tested a novel ATP competitive MEK inhibitor (MAP855) in this model. According to our knowledge this is the first patient derived cell line with this type of MEK mutation and the first spitzoid melanoma cell model. MethodsPF130 cell line was established from the pleural effusion sample of a 37-year-old male patient with spitzoid melanoma. NGS was used for mutational analysis. Cells were treated either with allosteric MEK inhibitor selumetinib or with newly developed ATP competitive MEK inhibitor MAP855. We analyzed changes in cell number, cell cycle distribution and ERK activation after treatment in vitro. Furthermore, the in vivo tumorigenicity was tested by injecting the cells subcutaneously, intrapleurally or intravenously into female SCID mice. ResultsWe found that ATP competitive MEK inhibitor MAP855 strongly decreased the viability of PF130 cells, while allosteric inhibitor selumetinib did not. Cell cycle analysis showed that MAP588 treatment could induce cell death in PF130 cells in a concentration dependent manner and slightly reduced the amount of cells in the S and the G2M phases. Furthermore, MAP855 was able to reduce ERK protein activation in PF130 cells effectively while selumetinib treatment had no effect. In vivo, intrapleurally injected cells established macroscopic tumors in the chest cavity after two months while intravenously and subcutaneously delivered cells showed limited growth. ConclusionsWe established a new cellular model of tumors with RAF- and phosphorylation independent MEK mutation. We found that recently developed ATP-competitive MEK inhibitor MAP855 is a potent inhibitor of these cells in vitro. The in vivo efficacy is currently under investigation. Furthermore, we describe here to the best of our knowledge the first patient derived spitzoid melanoma cell model to test both in vitro and in vivo novel therapeutic modalities. Legal entity responsible for the studyBalazs Hegedus. FundingHas not received any funding. DisclosureAll authors have declared no conflicts of interest.

Utility of p16-Ki-67-HMB45 score in sorting benign from malignant Spitz tumors

When Spitz nevi have increased vertical thickness (>1.0 mm), show ulceration and deep seated mitoses, the differential diagnostic considerations of atypical Spitz tumor (AST) or a Spitzoid melanoma (SM) enter into consideration. While molecular genetic testing could be employed in the work up of atypical melanocytic proliferations, they are expensive and not available at all institutions. Recently, one study employed the combination of p16, Ki-67 and HMB45 (PKH) immunohistochemistry on adult melanomas and proposed a combination of the three markers with scoring of their result to support a diagnosis of melanoma. We report the utility of this antibody combination scoring in discriminating SM and AST in children. We retrospectively reviewed 30 Spitzoid lesions (7 SM, 9 AST and 14 Spitz nevi) from children. Slides from H&E staining and Immunohistochemistry for p16, Ki-67 and HMB45 were reviewed for all cases. The extent of immunohistochemical expression in the lesional cells was scored following published criteria as follows: p16 scored as 0, 1, 2, 3; Ki-67 scored as 0, 1, 2, 3, 4 and HMB45 scored as 0, 1 and 2. Thus, the total PKH score for the combination of the 3 antibodies for any case could vary from 0 to 9. The result of the immunohistochemical analysis of cases in our study revealed that the PKH score of Spitz nevus and AST was below 4 for each of the case and that of SM was >4 for each of the case. These results are significant as the previously published study found that the PKH score of equal/or >4 correlated with melanoma and less <4 correlated with benign nevi. Independently, the immunostains could be misleading as Ki-67 labeling index tended to be higher in young children (<2 years of age) and HMB45 was occasionally negative in both AST and SM, and p16 could be completely lost in AST.Our study replicates the findings of the published study of adult melanomas and nevi that showed a total PKH score of equal/or>4 is seen in melanoma. Although, the number of SM cases in our study are few, the PKH scoring pattern of malignant and benign cases was congruent with the adult study. We suggest routine use of PKH immunohistochemistry in the work up of atypical Spitzoid lesions in children.

Abstract 731: Clinical genome sequencing uncovers potentially targetable truncations and fusions of MAP3K8 in spitzoid and other melanomas

Abstract Most melanomas arising in children and adolescents are of the spitzoid subtype. Unlike conventional melanomas in adults, spitzoid tumors are driven by fusions of kinase genes such as ALK, NTRK1/3, MET, RET and ROS1. However, in approximately 50% of cases, no oncogenic driver has been established. This raises the possibility of an, as yet, undescribed oncogene in such tumors. Clinical whole genome and transcriptome (RNA-Seq) sequencing detected a novel fusion of MAP3K8 in a spitzoid melanoma from an adolescent patient. The fusion preserved the kinase domain of MAP3K8 - a serine threonine kinase that activates MEK/ERK downstream - but replaced the autoinhibitory final exon with an unrelated gene, GNG2. MAP3K8 is a proposed oncogene in breast, ovarian, squamous cell carcinoma and lung cancer and its high expression has been shown to cause resistance to BRAF inhibitors through a MEK-dependent mechanism in melanoma cells (Johannessen et al. 2010 Nature 468:968-72). As the patient had exhausted other therapeutic options, we treated him with the MEK inhibitor, trametinib, and observed a transient response. He later relapsed, and further clinical sequencing showed the MAP3K8-GNG2 fusion had increased in genomic copy number and expression - potentially explaining the acquired resistance to trametinib. We subsequently screened a cohort of 49 pediatric melanomas with spitzoid features by RNA-Seq, fluorescence in situ hybridization and immunohistochemistry and found that MAP3K8 fusions and truncations were the most common genetic event, supplying the missing kinase driver for 33% of samples. All rearrangements preserved MAP3K8 exons 1-8 but replaced the autoinhibitory final exon with unrelated genetic or intergenic sequence. Strikingly, MAP3K8 rearrangements were mutually exclusive of other known driver mutations such as ALK fusions, further implicating MAP3K8 as a driver oncogene. Transformation assays using NIH 3T3 cells confirmed that the truncated form of MAP3K8 was oncogenic. Finally, we screened over 11,000 TCGA RNA-Seq samples, and identified seven adult melanomas with analogous MAP3K8 disruptions (1.5% of SKCM samples). Similar to their pediatric counterparts, all seven tumors lacked any other kinase driver mutation. Thus, MAP3K8 rearrangements drive a subset of adult melanomas and these tumors may also be amenable to MEK inhibition. Our experience highlights the need for genome-wide clinical sequencing as MAP3K8 is not covered by popular targeted gene panels. Citation Format: Scott Newman, Liying Fan, Allison Pribnow, Antonina Silkov, Stephen V. Rice, Seungjae Lee, Ying Shao, Bridget Shaner, Heather Mulder, Joy Nakitandwe, Sheila Shurtleff, Elizabeth Azzato, Gang Wu, Xin Zhou, Raymond Barnhill, John Easton, Kim E. Nichols, David W. Ellison, Downing R. James, Alberto Pappo, Philip M. Potter, Jinghui Zhang, Armita Bahrami. Clinical genome sequencing uncovers potentially targetable truncations and fusions of MAP3K8 in spitzoid and other melanomas [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 731.

The Amount of Melanin Influences p16 Loss in Spitzoid Melanocytic Lesions: Correlation With CDKN2A Status by FISH and MLPA.

The risk assessment of spitzoid lesions is one of the most difficult challenges in dermatopathology practice. In this regard, the loss of p16 expression and the homozygous deletion of CDKN2A, have been pointed in the literature as reliable indicators of high risk. However, these findings are poorly reproducible, and the molecular bases underlying the loss of p16 expression remain unclear. We aimed to identify the underlying events causing loss of CDKN2A/p16 in spitzoid tumors. We evaluated the immunohistochemical expression of p16, and the presence of CDKN2A genetic alterations detected through fluorescence in situ hybridization (FISH) and multiplex ligation-dependent probe amplification (MLPA), in a series of 130 Spitz nevi, 20 atypical spitzoid tumors, and 11 spitzoid melanoma. We found a significant loss of p16 expression in cases with high amount of melanin content in the 3 groups (P<0.000001) and a similar proportion of p16-negative cases in the group of Spitz nevi and atypical spitzoid tumors. MLPA allowed the recognition of CDKN2A microdeletions, which correlated with p16 loss (P=0.01). MLPA and FISH were more accurate than immunohistochemistry to detect CDKN2A alterations; although contrary to MLPA, FISH fails to recognize CDKN2A microdeletions. According to our results, p16 expression may be useful in the study of cases with atypical features and low melanin content, but it has no value in highly pigmented spitzoid lesions.

Nestin Expression in Spitzoid Lesions: An Immunohistochemical Characterization With Clinical and Dermoscopic Correlations

Spindle or epithelioid melanocytic (Spitz) nevi usually affect children or adolescents and growth in the face or the lower extremities. Histologically, they may show cytoarchitectural atypia and mitotic figures that could represent diagnostic pitfalls with malignant melanoma. Atypical spitzoid tumors (AST) indicate lesions that microscopically show intermediate characteristics between benign nevi and malignant melanoma. Nestin expression has been evaluated in benign nevi and malignant melanoma, but no studies on its role in Spitz lesion have been elaborated so far. Our results indicate that Nestin could allow to discriminate between AST and malignant spiztoid melanoma; the typical dermoscopic pattern is also associated with benign nevi in contrast to the atypical pattern that accumunates AST and malignant spitzoid melanoma.

Potentially Actionable MAP3K8 Alterations Are Common in Spitzoid Melanoma

Fusions or truncations of MAP3K8 occur in 33% of spitzoid melanomas and 1.5% of adult melanomas.

Spitzoid cutaneous melanoma is associated with favorable clinicopathological factors and outcome.

Spitzoid melanoma is one of the rare subtypes of melanoma, whose clinical and pathological characteristics have yet to be understood. Understanding the histopathologic features and behavior characteristics of Spitzoid cutaneous melanoma. A total number of 11 Turkish Caucasian patients with pathologically diagnosed Spitzoid melanoma were analyzed retrospectively. The median age of patients was 24years (ranging from 16 to 54years), and the females outnumbered the males (90%). The extremities, especially lower limbs (67%), were the most commonly affected primary areas (64% of patients). Median depth and mitotic rate were 2.2mm and 3/mm2 , respectively. The presence of ulceration and regression were observed in a few lesions (14%). While tumor-infiltrating lymphocytes were expressed in all of the lesions, none of the lesions was associated with lymphovascular invasion and/or neurotropism. The regional lymph nodes were involved only in minority of the patients (27%), and no patients had metastatic disease. Recurrences occurred in only two patients (18%) that affected merely distant areas, that is, lung and brain. The median disease-free survival time and 5-year disease-free survival rate were 20.5months and 80.6%, respectively. Only one (9%) death occurred; and the median overall survival time was 26.2months, and 5-year overall survival rate was 90.7%. Spitzoid cutaneous melanoma is correlated with favorable histopathologic and clinical characteristics, and therefore, it is associated with better survival rates.

Activating Structural Alterations in MAPK Genes Are Distinct Genetic Drivers in a Unique Subgroup Of Spitzoid Neoplasms.

Recent studies have described kinase fusions as the most common initiating genomic events in Spitzoid neoplasms. Each rearrangement generates a chimeric protein with constitutive activation of the tyrosine kinase domain, resulting in the development of a Spitzoid neoplasm. Identifying key initiating genomic events and drivers may assist in diagnosis, prognostication, and management. Retrospective, consecutive search of our database between 2009 and 2018 for Spitzoid neoplasms identified 86 cases. Whole transcriptome mRNA and DNA sequencing (1714 genes) detected 9% of cases (8/86) with structural rearrangements in MAPK genes other than BRAF and 47% (40/86) with kinase fusions previously described in Spitzoid neoplasms. We identified in-frame fusions of MAP3K8-DIPC2, MAP3K8-PCDH7, MAP3K8-UBL3, MAP3K8-SVIL (n=6), and ATP2A2-MAP3K3 (n=1) as well as a p.I103_K104 in-frame deletion of MAP2K1 (n=1), in the absence of well-recognized drivers of melanocytic neoplasia. Fluorescence in situ hybridization validated all cases (n=7) with available tissue. Cases occurred in younger patients (median age 18 y). Morphologically, cases were predominantly epithelioid (P=0.0032), often with some melanin pigment (P=0.0047), and high-grade nuclear atypia (P=0.012). A significant proportion were thought to be Spitzoid melanomas (3/8). Average follow-up time was 11 months. One MAP3K8-DIP2C Spitzoid melanoma involved 4/5 sentinel lymph nodes and led to a complete lymph node dissection with unremarkable follow-up at 9 months. One MAP3K8-DIPC2 atypical Spitz tumor raised concern for recurrence at 10 months and was reexcised. We present a distinct subtype of Spitzoid neoplasm characterized by structural alterations in MAPK genes, which are important to recognize given the potential for treatment with MAPK inhibitors in metastatic cases.

Fusion of ALK to the melanophilin gene MLPH in pediatric Spitz nevi

Spitzoid neoplasms typically affect young individuals and include Spitz nevus, atypical Spitz tumor, and Spitzoid melanoma. Spitz tumors can exhibit gene fusions involving the receptor tyrosine kinases NTRK1, NTRK3, ALK, ROS1, RET, or MET, or the serine-threonine kinase BRAF. Because most studies have been based on adult cases, we studied ALK fusions in Spitz nevi occurring in pediatric patients. Twenty-seven cases were screened for ALK expression by immunohistochemistry, and 6 positive cases were identified. These cases were studied further using the TruSight RNA Fusion Panel, and in 4 cases, exon 20 of the ALK gene was found to be fused to exon 14 of the MLPH (melanophilin) gene, a gene fusion that has only been reported in a Spitz nevus in an adult. The remaining 2 cases showed no fusion of ALK with any gene. The cases with the MLPH-ALK fusion showed a similar histology to that described for Spitz nevi with ALK fusions, with spindle-shaped and epithelioid melanocytes in fusiform nests with a plexiform growth pattern and infiltrative border. We created a breakapart fluorescence in situ hybridization assay for MLPH, and all 4 cases with the MLPH-ALK fusion were positive, whereas the other 23 cases in the study were negative. Thus, ALK and MLPH were fused only to each other in our series. Melanophilin is part of the melanosome trafficking apparatus together with MYO5a, TPM3, and RAB27a, all constitutively expressed in melanocytes. Kinase fusions involving MYO5A and TPM3 have been reported in Spitz tumors, and our series adds MLPH to this group.

Expression of p15 in a spectrum of spitzoid melanocytic neoplasms.

Accurate classification of spitzoid melanocytic lesions is difficult due to overlapping clinical and histopathologic features between Spitz nevi, atypical Spitz tumors (ASTs), and spitzoid melanomas. Expression of p16 (CDKN2A) has been used as a marker of spitzoid lesions. However, its expression may be variable. p15 is a tumor suppressor encoded by CDKN2B, loss of which has been recently shown to promote transition from nevus to melanoma. We sought to determine whether p15 is a useful immunohistochemical marker to distinguish Spitz nevi from spitzoid melanomas and to compare p15 and p16 staining in this population. Immunohistochemistry for p15 and p16 was performed on Spitz nevi (n = 19), ASTs (n = 41), and spitzoid melanomas (n = 17). Immunoexpression was categorized by a four-tiered system: 0 (negative), 1+ (weak), 2+ (moderate), 3+ (strong). 3+/strong p15 staining was observed in 68.4% of Spitz nevi, 34.2% of ASTs, and 17.7% of spitzoid melanomas. By contrast, we observed 3+ p16 staining in roughly equivalent percentages of Spitz nevi (57.9%), ASTs (56.1%), and spitzoid melanomas (58.8%). These data illustrate that p15 may be more useful than p16 as a biomarker to help distinguish benign from malignant spitzoid lesions.

Dermoscopy of Spitz/Reed naevi and management.

Since their first description by Sophie Spitz, Spitz nevi have been a subject of controversy among clinicians for many decades, and remain a clinical conundrum until today as their etiology, morphology, biological behavior and natural evolution is still not totally clear. This is because their clinical, dermoscopic and histopathologic features sometimes overlap with those of melanoma, rendering the management of spitzoid lesions particularly difficult. In addition, cases of histopatologically equivocal lesions do exist and their classification might sometimes be very challenging. Among several terms that have been used to describe these morphologically "intermediate" lesions, atypical Spitz tumor (AST) is the most widely used. The aim of this review paper was to describe the dermoscopic patterns and structures seen in Spitz/Reed nevi, spitzoid melanoma and AST. Finally, this article provides an evidence-based update on the available options for the management of spitzoid lesions, before and after histopathologic diagnosis.

Spitzoid melanoma with ALK copy number gain

Spitzoid melanoma is an uncommon melanoma (type of skin cancer) that can occur at any age, and can resemble a harmless mole called a ‘Spitz nevus’. This similarity can make it difficult to diagnose. Spitzoid tumours (Spitz nevi) have recently begun to be categorized according to their genetic profile, meaning the genes found in them, and certain molecular alterations were found to link to changes to the structure of the nevus as could be seen when examined under a microscope. For example, Spitz tumours can have what is called an anaplastic lymphoma kinase (ALK) gene rearrangement. ALK is a gene that tells your body how to make proteins that help cells talk to each other. ALK rearrangement means that part of this gene is broken and attached to another gene. Spitz tumours with ALK rearrangement have been shown to have a distinctive “plexiform pattern”. Humans have two copies of most genes, but occasionally alterations can lead to the gain or a loss of one copy. When it is a gain of one copy this is called copy gain. In this report, authors from the US discuss a case of an 87‐year‐old man with a 3cm tumour on his back, and conclude that ALK copy gain represents an additional mechanism of ALK activation among Spitzoid tumours and shows the same plexiform pattern seen among ALK‐rearranged Spitz tumours.

Spitzoid melanoma in a child with xeroderma pigmentosum

Xeroderma pigmentosum (XP) is an autosomal recessive condition associated with a marked increase in the development of malignancies. We report a 10 year girl with freckles, lentigens and keratosis on the face and neck which had gradually developed from the age of two. History of marked photophobia was present. Few months prior she developed single firm, pigmented, non-tender, freely- mobile, sessile nodule over left ala of nose. Multiple frecklings with atrophic hypopigmented patches were distributed all over face and sparsely on neck. Histopathology examination (HPE) from growth over nasal ala revealed malignant tumour composed of spindloid to epithelioid cells arranged in sheets and nests in dermis suggestive of spitzoid melanoma. Fine needle aspiration cytology (FNAC) from left post-auricular lymph nodes revealed high cellularity comprising of many pleomorphic cells in clusters having enlarged irregular hyperchromatic nuclei. Wide local excision was done with nasolabial transposition of flap cover.

Clinicopathologically problematic melanocytic tumors: a case-based review.

BackgroundIn spite of recent advances in the histopathological and molecular diagnosis of melanocytic neoplasms, a certain proportion of these lesions remain a daunting challenge for both the clinician and the pathologist.ObjectivesTo emphasize the importance of close collaboration between clinicians and pathologists in case of problematic melanocytic lesions.PatientsWe report and discuss 5 problematic scenarios of melanocytic lesions, including tumoral melanosis, nevoid melanoma, lentiginous melanoma, spitzoid melanoma and BAPoma that may pose diagnostic difficulties in our practice.ConclusionsClinico-dermoscopic-pathological correlation, with incorporation of all the available data, in problematic melanocytic skin neoplasms is of paramount importance for accurate diagnosis.

The role of routine imaging in pediatric cutaneous melanoma.

Optimal imaging for children with pediatric malignant melanoma (MM) is unknown. We reviewed clinical and imaging findings of patients with American Joint Commission on Cancer (AJCC) stage IIC-IV MM treated on our institutional MEL06 trial. All patients had baseline brain magnetic resonance imaging/computed tomography (MRI/CT), positron emission tomography/computed tomography (PET/CT), CT chest, abdomen, and pelvis (CTCAP). Patients on stratum A (PEG-interferon, where PEG is pegylated; AJCC IIC, IIIA, IIIB; n=16) had imaging every 6months; stratum B1 (PEG-interferon and temozolomide; unresectable measurable disease, metastatic, or recurrent; n=2) had PET/CT scans every 2months and brain imaging studies every 4months; stratum B2 patients (PEG-interferon and temozolomide; unresectable nonmeasurable, metastatic, or recurrent, n=3) had imaging every 4months. Off-therapy imaging was done every 6 months for 3 years. There were 21 patients (11 females, 11 spitzoid, median age 14years, head/neck [6], trunk [7], extremities [8]). Patients with spitzoid melanoma underwent 236 imaging studies in total (86 PET/CT, 81 CTCAP, 11 CT chest, 10 CT brain, 48 MRI brain) at a median cost per patient of $32,718. Thirteen studies (5.8%) had findings that led to two biopsies (one positive). For conventional MM, 162 studies (61 PET/CT, 57 CTCAP, 8 CT chest, 7 CT brain, and 29 MRI brain) were performed with a median cost per patient of $23,420. Twenty (14%) had findings leading to six biopsies (four positive). At 6.3years (range 0.4-9.2), 17 patients remain disease-free. Children with spitzoid melanoma require minimal imaging at diagnosis and follow-up. Patients with conventional MM should be imaged according to adult guidelines.

Genomic Fusions in Pigmented Spindle Cell Nevus of Reed.

Recent molecular studies of spitzoid neoplasms have identified mutually exclusive kinase fusions involving ROS1, ALK, RET, BRAF, NTRK1, MET, and NTRK3 as early initiating genomic events. Pigmented spindle cell nevus (PSCN) of Reed is a morphologic variant of Spitz and may be very diagnostically challenging, having histologic features concerning for melanoma. Their occurrence in younger patients, lack of association to sun exposure, and rapid early growth phase similar to Spitz nevi suggest fusions may also play a significant role in these lesions. However, to date, there is little data in the literature focused on the molecular characterization of PSCN of Reed with next-generation sequencing. We analyzed a total of 129 melanocytic neoplasms with RNA sequencing including 67 spitzoid neoplasms (10 Spitz nevi, 44 atypical Spitz tumors, 13 spitzoid melanomas) and 23 PSCN of Reed. Although only 2 of 67 (3.0%) of spitzoid lesions had NTRK3 fusions, 13 of 23 (57%) of PSCN of Reed harbored NTRK3 fusions with 5' partners ETV6 (12p13) in 2 cases and MYO5A (15q21) in 11 cases. NTRK3 fusions were confirmed with a fluorescent in situ hybridization break-apart probe. The presence of a NTRK3 fusion correlated with younger age (P=0.021) and adnexal extension (P=0.001). Other minor fusions identified in PSCN of Reed included MYO5A-MERTK (2), MYO5A-ROS1, MYO5A-RET, and ETV6-PITX3 leading to a total of 78% with fusions. Our study suggests that the majority of PSCN of Reed are the result of genomic fusions, and the most frequent and characteristic genomic aberration is an NTRK3 fusion.

Prevalence of ALK gene alterations among the spectrum of plexiform spitzoid lesions

ALK receptor tyrosine kinase gene (ALK) rearrangements have been described in spitzoid lesions with a plexiform growth pattern. To investigate the prevalence of ALK alterations in a large series of spitzoid lesions. ALK immunohistochemical and fluorescence in situ hybridization analyses of 78 spitzoid plexiform lesions including 41 Spitz nevi, 29 atypical Spitz tumors (ASTs), and 8 spitzoid melanomas. ALK immunohistochemical staining was observed in 14.6% of Spitz nevi (6 of 41) and 13.8% of ASTs (4 of 29); the spitzoid melanomas were ALK negative. Fluorescence in situ hybridization confirmed ALK translocation in 9 cases and amplification in 1 case. In 2 of the translocated cases it was possible to determine the fusion partner gene (ie, tropomyosin 3 gene [TPM3] or dynactin 1 gene [DCTN1]). Of the 4 cases of AST examined, 2 carried the B-Raf proto-oncogene, serine/threonine kinase gene (BRAF) V600E mutation. The 10 patients had a mean age of 18.7years (range, 1-39) and a female predominance (female-to-male ratio, 7:3). Seven lesions arose on the extremities; the 2 lesions occurring in infants were located on the face. The lesions' mean diameter was 6.2mm (range, 3-13), and their mean Breslow thickness was 1.83mm (range, 0.6-3.6). The results of sentinel node biopsy were negative in 2 ASTs. BRAF status was tested in only 4 of 10 samples because of the limited amount of material. ALK alterations characterize a significant subset of spitzoid lesions.

The difficulty in interpreting gene expression profiling in BAP-negative melanocytic tumors.

BAP-negative melanocytic tumors were unrecognized in the medical literature until 2011. While the clinical significance of these tumors is poorly understood, there is concern such lesions represent processes in transition, and malignant degeneration is a concern. We investigated use of a 23-gene expression profiling (23-GEP) test for distinction from melanoma with the aim of better characterizing the biologic potential of such tumors. Twenty BAP-negative melanocytic tumors, subjected to 23-GEP (Myriad Genetic Laboratories, Inc. [Salt Lake City, Utah]) testing, were retrospectively analyzed. Tumors exhibited varying degrees of atypia and aberrant immunohistochemical profiles. 23-GEP testing revealed a "malignant" genetic signature in four cases, a "benign" signature in 15 cases, and an "indeterminate" signature in one case. Array-based comparative genomic hybridization (aCGH) testing was performed for two cases with a "malignant" 23-GEP signature, but the aCGH result conflicted with 23-GEP, and supported benignity. Conversely, in one case with a "benign" 23-GEP result, aCGH testing supported assessment as melanoma. Moreover, evolving melanoma could not be wholly excluded by histopathological analysis in 2 "benign" cases. BAP-negative melanocytic tumors remain a diagnostic dilemma for dermatopathologists. A widely marketed 23-GEP test may not be useful in distinguishing these tumors from spitzoid melanoma, at least in comparison to aCGH technology.

An update on molecular alterations in melanocytic tumors with emphasis on Spitzoid lesions.

Significant progress in the molecular pathology of melanocytic tumors have revealed that benign neoplasms, so-called nevi, are initiated by gain-of-function mutations in one of several primary oncogenes, such as BRAF in acquired melanocytic nevi, NRAS in congenital nevi or GNAQ/GNA11 in blue nevi, with consequent MAPK and PI3K/AKT/mTOR activation. Secondary genetic alterations overcome tumor suppressive mechanisms and allow the progression to intermediate lesions characterized by TERT-p mutation or to invasive melanomas displaying disruption of tumor suppressor genes. Currently, melanoma is molecularly regarded as four different diseases, namely BRAF, NRAS, NF1 and the "triple wild type" subtypes, which are associated with particular clinicopathological features. Melanocytic Spitzoid lesions include benign Spitz nevus, atypical Spitz tumor (AST) and Spitzoid melanoma. This is a challenging diagnostic group, particularly with regard to the distinction between AST and Spitzoid melanoma on clinical and histological grounds. Molecular analysis has identified the presence of HRAS mutation, BAP1 loss (often accompanying by BRAF mutations) or several kinase fusions in distinct categories of Spitz tumors. These aberrations account for the rapid growth characteristic of Spitz nevi. Subsequent growth is halted by various tumor suppressive mechanisms abrogation of which allow the development of AST, now better classified as low-grade melanocytic tumor. Although at present ancillary genetic techniques have not been very helpful in the prediction of biological behavior of AST, they have defined distinct tumor subsets differing with regard to biology and histology. Finally, we discuss how novel molecular markers may assist the differential diagnosis of melanoma, particularly from malignant peripheral nerve sheath tumor (MPNST). It is anticipated that the significant progress in the field of molecular pathology regarding the various types of melanocytic tumors, will eventually contribute to a more accurate histologic categorization, prediction of biologic behavior and personalized treatment.