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International audience; Aims: Recently, YAP1 fusion genes have been demonstrated in eccrine poroma and porocarcinoma, and the diagnostic use of YAP1 immunohistochemistry has been highlighted in this setting. In other organs, loss of YAP1 expression can reflect YAP1 rearrangement or transcriptional repression, notably through RB1 inactivation. In this context, our objective was to re-evaluate the performance of YAP1 immunohistochemistry for the diagnosis of poroma and porocarcinoma.Methods and results: The expression of the C-terminal part of the YAP1 protein was evaluated by immunohistochemistry in 543 cutaneous epithelial tumours, including 27 poromas, 14 porocarcinomas and 502 other cutaneous tumours. Tumours that showed a lack of expression of YAP1 were further investigated for Rb by immunohistochemistry and for fusion transcripts by real-time PCR (YAP1::MAML2 and YAP1::NUTM1). The absence of YAP1 expression was observed in 24 cases of poroma (89%), 10 porocarcinoma (72%), 162 Merkel cell carcinoma (98%), 14 squamous cell carcinoma (SCC) (15%), one trichoblastoma and one sebaceoma. Fusions of YAP1 were detected in only 16 cases of poroma (n = 66%), 10 porocarcinoma (71%) all lacking YAP1 expression, and in one sebaceoma. The loss of Rb expression was detected in all cases except one of YAP1-deficient SCC (n = 14), such tumours showing significant morphological overlap with porocarcinoma. In-vitro experiments in HaCat cells showed that RB1 knockdown resulted in repression of YAP1 protein expression.Conclusion: In addition to gene fusion, we report that transcriptional repression of YAP1 can be observed in skin tumours with RB1 inactivation, including MCC and a subset of SCC.

The histopathological assessment of diagnostically ambiguous melanocytic proliferation remains one of the biggest challenges in the dermatopathology field. Preferentially expressed Antigen in MElanoma (PRAME) immunostaining has been shown highly specific for distinguishing unequivocal malignant melanocytic proliferation from benign ones. Knowledge on its utility for evaluating ambiguous melanocytic neoplasms remains limited. We retrieved in our institutional database all cases of diagnostically ambiguous melanocytic neoplasms from January 2016 to January 2021. Each case was subclassified into "favor benign" or "favor malignant" neoplasm using all collected data. Immunohistochemical expression of PRAME was assessed and correlated with the final subclassification. Using a previously proposed scoring system, diffuse immunopositivity (75% of tumor cells) was considered positive. Furthermore, for ambiguous melanocytic proliferation occurring on a pre-existing nevus, the staining was considered positive if more than 75% of the morphologically atypical neoplastic cells were labeled, excluding morphologically unambiguous benign nevocytes. Fifty-five cases of ambiguous melanocytic proliferation were examined. Thirty-one cases were finally subclassified as "favor malignant" neoplasms and 24 as "favor benign" neoplasms. Thirty-one tumors showed immunopositivity for PRAME, representing, respectively, 8.3% and 93.5% of "favor benign" and "favor malignant" neoplasms. The specificity and sensitivity of PRAME immunohistochemistry for benign/malignant distinction were, respectively, 91.7% and 93.5%.PRAME IHC shows high sensitivity and specificity for distinguishing malignant challenging melanocytic proliferations from benign ones and could be used as an everyday tool. However, PRAME immunoreactivity should be interpreted cautiously, knowing that rare benign melanocytic neoplasms could show diffuse positivity.

Introduction: Despite advances in the understanding of the molecular pathogenesis of cutaneous melanoma, relatively little is known about the genetic changes that occur in the progression of conjunctival melanocytic intraepithelial lesions to invasive conjunctival melanoma. Methods: We exposed 4 exenteration specimens that each contained varying grades of intraepithelial conjunctival melanocytic neoplasia and invasive neoplasia to a combination of various techniques, including array comparative genomic hybridization (aCGH), ribonucleic acid sequencing (RNA-seq), fluorescence in situ hybridization (FISH), and immunohistochemistry. Results: Three out of 4 of the invasive melanomas showed gains in 11q13 (CCND1 locus) by aCGH. FISH demonstrated CCND1 gain in invasive melanoma and in conjunctival melanocytic intraepithelial lesions (CMILs) of all grades (low-grade CMILs and in situ melanoma), and this was paralleled by increased expression of Cyclin D1 protein within the atypical melanocytes by immunohistochemistry, using a double-staining method with a red end point for Melan A cytoplasmic staining and a brown end point for nuclear Cyclin D1 expression. Higher grades of melanocytic intraepithelial lesions showed more cells expressing Cyclin D1 than lower grade melanocytic intraepithelial lesions. The Cyclin D1 protein expression was in the same location as the amplified CCND1 signal by FISH. One out of 3 of these cases also showed the amplification of the 12q13-15 locus corresponding to MDM2 and FISH confirmed gains in the conjunctival melanocytic intraepithelial neoplasia and invasive melanoma. The remaining fourth case showed a homozygous deletion of 9p21 (CDKN2A) by aCGH only, with immunohistochemistry showing clonal loss of p16 protein expression in the invasive and conjunctival melanocytic intraepithelial lesion. Two out of 4 of the invasive melanomas harboured classical driver mutations in NRAS and NF-1, respectively. None of the cases showed mutations in BRAF, KIT, and TERT mutations. RNA-seq data showed secondary mutations in ARAF, PLCB4, MET, EZH2, MAP2K2, CTNNB1, CIITA, NF2, TP53, and MEN1, some of which are implicated in the MAPK pathway. Conclusion: CMILs harbour amplifications of CCND1 (3 cases), MDM2 (1 case), and loss of CDKN2A (1 case), which are also present when the lesion progresses to invasive melanoma, implicating these amplifications in the early pathogenesis of CMILs. This study represents the first attempt to capture the mutational landscape of all stages of conjunctival melanoma in a single tissue excision.

The WHO classification identifies nine classes of melanocytic proliferations according to location, UV exposure, histological, and genetic features. Only a minority of lesions remain unclassified. We describe five cases that harbored either an ERBIN-RASGRF2 or an ATP2B4-RASGRF2 in-frame fusion transcript. These lesions were collected from different studies, unified only by the lack of identifiable known mutations, with a highly variable phenotype. One case was a large abdominal congenital nevus, three were slowly growing pigmented nodules, and the last was an ulcerated nodule arising on the site of a preexisting small nevus, known since childhood. The latter was diagnosed as a 4 mm thick melanoma with loss of BAP1 expression. The four other cases were compound, melanocytic proliferations with an unusual deep pattern of small dense nests of bland melanocytes encased in a fibrous background. The RASGRF2 fusion was confirmed by a break-apart FISH technique. Array CGH performed in three cases found non-recurrent secondary copy number alterations. Follow-up was uneventful. In silico analysis identified a single RASGRF2 fusion in the TCGA pan-cancer database, whereas RASGRF2 variants were stochastically distributed in all cancer subtypes.

Atypical Spitzoid melanocytic tumors are diagnostically challenging. Many studies have suggested various genomic markers to improve classification and prognostication. We aimed to assess whether next-generation sequencing studies using the Tempus xO assay assessing mutations in 1711 cancer-related genes and performing whole transcriptome mRNA sequencing for structural alterations could improve diagnostic agreement and accuracy in assessing neoplasms with Spitzoid histologic features. Twenty expert pathologists were asked to review 70 consultation level cases with Spitzoid features, once with limited clinical information and again with additional genomic information. There was an improvement in overall agreement with additional genomic information. Most significantly, there was increase in agreement of the diagnosis of conventional melanoma from moderate (κ=0.470, SE=0.0105) to substantial (κ=0.645, SE=0.0143) as measured by an average Cohen κ. Clinical follow-up was available in all 70 cases which substantiated that the improved agreement was clinically significant. Among 3 patients with distant metastatic disease, there was a highly significant increase in diagnostic recognition of the cases as conventional melanoma with genomics (P

The recent WHO classification of skin tumors has underscored the importance of acknowledging intermediate grade melanocytic proliferations. A multistep acquisition of oncogenic events drives the progressive transformation of nevi into melanomas. The various pathways described are modulated by the initial oncogenic drivers that define the common, blue, and Spitz nevi groups. Intermediate lesions are most often the result of a clonal evolution within such nevi. Based on this established classification, we have suggested for each pathway a practical diagnostic approach, benefiting from the recently developed molecular tools, both in the setting of general pathology labs and expert centers. Moreover, recommendations regarding the re-excision and clinical follow-up are given to support decision-making in multidisciplinary tumor boards.

Fusions of ALK, ROS1, NTRK1, NTRK3, RET, MET, MERTK, FGFR1, ERBB4, LCK, BRAF, MAP3K8, MAP3K3, and PRKDC and mutation of HRAS have so far been discovered as the genetic alterations associated with the pathogenesis of Spitz neoplasms. This report presents the first case of NTRK2-rearranged Spitz/Reed nevus. The patient was a 39-year-old male with a pigmented macule rapidly growing on his shoulder. Histopathologically, the lesion was a junctional melanocytic nevus composed of large nests of spindled melanocytes with abundant eosinophilic cytoplasm associated with a hyperplastic epidermis. These findings fulfilled the diagnostic criteria of a pigmented spindle cell nevus of Reed (variant of Spitz nevus). Immunohistochemistry for pan-Trk revealed diffuse cytoplasmic positivity in the tumor cells, but immunoexpression of ALK, ROS1, and BRAF V600E was not seen. A novel, in-frame, TFG-NTRK2 fusion was identified by RNA sequencing. This case report expands the list of genetic alterations in Spitz neoplasms and the spectrum of NTRK2-rearranged tumors.

Spitz tumors are genetically associated with activating HRAS point mutations or fusions of either ALK, ROS1, NTRK1, NTRK3, RET, MET, MERTK, LCK, BRAF, MAP3K8, or MAP3K3. All these driver gene alterations are mutually exclusive. We report two cases of agminated Spitz naevi with a GOPC-ROS1 fusion. Both cases occurred on the lower limb of young adults. Since adolescence, pigmented or pink-colored papules have been periodically arising in a limited area of skin. In one case, an ill-defined hyperpigmented macule known since childhood was present in the background. Morphologically, at least five lesions were analyzed from each patient. In one case, all were predominantly junctional pigmented Spitz naevi, and in the other case, all were compound unpigmented Spitz naevi. No atypical features were present. RNA-sequencing revealed a GOPC-ROS1 gene translocation in both cases. Split signals of ROS1 gene in fluorescence in situ hybridization were observed not only in the nests of spitzoid melanocytes but also in the bland basal melanocytes surrounding the proliferations. These findings suggest the presence of a GOPC-ROS1 mosaicism in melanocytes with further emergence of agminated Spitz naevi potentially triggered by other genetic alterations. This expands the spectrum of genetic anomalies described in agminated Spitz naevi and our understanding of the mechanisms involved in their emergence.

The genetic anomalies associated with the agminated variant of Spitz nevus have so far been limited to HRAS G13R mutations, especially when arising within a nevus spilus. A previous report exposed the case of a man with a giant pigmented macule involving his upper right limb and trunk. Since childhood, Spitz nevi have been periodically arising, within the pigmented area. The histopathology of several lesions displayed the usual criteria of junctional, compound, or intradermal Spitz nevi with a diversity of cytomorphological and architectural features. Some lesions spontaneously regressed. Genetic studies confirmed in three lesions an identical translocation involving TRPM1, PUM1, and LCK. No mutations in HRAS, NRAS, BRAF, or other known fusion genes linked to Spitz nevus were detected. LCK break-apart fluorescence in situ hybridization confirmed the rearrangement was present not only in the melanocytic proliferation but also in the surrounding non-spitzoid melanocytes. This report expands the list of genetic alterations involved both in giant congenital macules and in agminated Spitz nevi, and also extends the concept of mosaicism in melanocytes to gene translocations.

BackgroundThe efficacy of immunotherapies in metastatic melanoma depends on a robust T cell infiltration. Oncogenic alterations of tumor cells have been associated to T cell exclusion. Identifying novel cancer cell-intrinsic non-genetic mechanisms of immune escape, the targeting of which would reinstate T cell recruitment, would allow to restore the response to anti-programmed cell death protein 1 (PD-1) antibody therapy. The epithelial-to-mesenchymal transition (EMT)-inducing transcription factor ZEB1 is a major regulator of melanoma cell plasticity, driving resistance to mitogen-activated protein kinase (MAPK) targeted therapies. We thus wondered whether ZEB1 signaling in melanoma cells may promote immune evasion and resistance to immunotherapy.MethodsWe evaluated the putative correlation between ZEB1 expression in melanoma cells and the composition of the immune infiltrate in a cohort of 60 human melanoma samples by combining transcriptomic (RNA-sequencing) and seven-color spatial multi-immunofluorescence analyses. Algorithm-based spatial reconstitution of tumors allowed the quantification of CD8+, CD4+ T cells number and their activation state (PD-1, Ki67). ZEB1 gain-of-function or loss-of-function approaches were then implemented in syngeneic melanoma mouse models, followed by monitoring of tumor growth, quantification of immune cell populations frequency and function by flow cytometry, cytokines secretion by multiplex analyses. Chromatin-immunoprecipitation was used to demonstrate the direct binding of this transcription factor on the promoters of cytokine-encoding genes. Finally, the sensitivity to anti-PD-1 antibody therapy upon ZEB1 gain-of-function or loss-of-function was evaluated.ResultsCombined spatial and transcriptomic analyses of the immune infiltrates in human melanoma samples demonstrated that ZEB1 expression in melanoma cells is associated with decreased CD8+ T cell infiltration, independently of β-catenin pathway activation. ZEB1 ectopic expression in melanoma cells impairs CD8+ T cell recruitment in syngeneic mouse models, resulting in tumor immune evasion and resistance to immune checkpoint blockade. Mechanistically, we demonstrate that ZEB1 directly represses the secretion of T cell-attracting chemokines, including CXCL10. Finally, Zeb1 knock-out, by promoting CD8+ T cell infiltration, synergizes with anti-PD-1 antibody therapy in promoting tumor regression.ConclusionsWe identify the ZEB1 transcription factor as a key determinant of melanoma immune escape, highlighting a previously unknown therapeutic target to increase efficacy of immunotherapy in melanoma.Trial registration numberNCT02828202.

ImportanceA standardized pathology classification system for melanocytic lesions is needed to aid both pathologists and clinicians in cataloging currently existing diverse terminologies and in the diagnosis and treatment of patients. The Melanocytic Pathology Assessment Tool and Hierarchy for Diagnosis (MPATH-Dx) has been developed for this purpose.ObjectiveTo revise the MPATH-Dx version 1.0 classification tool, using feedback from dermatopathologists participating in the National Institutes of Health–funded Reducing Errors in Melanocytic Interpretations (REMI) Study and from members of the International Melanoma Pathology Study Group (IMPSG).Evidence ReviewPracticing dermatopathologists recruited from 40 US states participated in the 2-year REMI study and provided feedback on the MPATH-Dx version 1.0 tool. Independently, member dermatopathologists participating in an IMPSG workshop dedicated to the MPATH-Dx schema provided additional input for refining the MPATH-Dx tool. A reference panel of 3 dermatopathologists, the original authors of the MPATH-Dx version 1.0 tool, integrated all feedback into an updated and refined MPATH-Dx version 2.0.FindingsThe new MPATH-Dx version 2.0 schema simplifies the original 5-class hierarchy into 4 classes to improve diagnostic concordance and to provide more explicit guidance in the treatment of patients. This new version also has clearly defined histopathological criteria for classification of classes I and II lesions; has specific provisions for the most frequently encountered low–cumulative sun damage pathway of melanoma progression, as well as other, less common World Health Organization pathways to melanoma; provides guidance for classifying intermediate class II tumors vs melanoma; and recognizes a subset of pT1a melanomas with very low risk and possible eventual reclassification as neoplasms lacking criteria for melanoma.Conclusions and RelevanceThe implementation of the newly revised MPATH-Dx version 2.0 schema into clinical practice is anticipated to provide a robust tool and adjunct for standardized diagnostic reporting of melanocytic lesions and management of patients to the benefit of both health care practitioners and patients.

Background: Melanoma is a type of cancer with robust response to immunotherapy. Programmed death ligand 1 (PD-L1) testing is not required to treat patients, but most studies have demonstrated correlations between PD-L1 expression and treatment response using various assays and scoring methods. This multicenter study aimed to harmonize PD-L1 immunohistochemistry (IHC) and scoring in melanoma. To provide a reference for PD-L1 expression independent of the IHC protocol, PD-L1 mRNA expression was determined via RNAscope, then compared to IHC.Methods: Standardized PD-L1 assays (22C3, 28–8, SP142, and SP263) and laboratory-developed tests (clone QR1 and 22C3) were evaluated on three IHC platforms using a training set of 7 cases. mRNA expression was determined via RNAscope (CD274/PD-L1 probe) and analyzed by image analysis. PD-L1 IHC findings were scored by seven blinded pathologists using the tumor proportion score (TPS), combined positive score (CPS), and MELscore. After the study, a standardized method was proposed; this was validated by three blinded pathologists on a set of 40 metastatic melanomas that were stained using three protocols.Results: Concordances among various antibody/platforms were high across antibodies (e.g., intraclass correlation coefficient [ICC] > 0.80 for CPS), except for SP142. Two levels of immunostaining intensities were observed: high (QR1 and SP263) and low (28–8, 22C3, and SP142). Reproducibilities across pathologists were higher for QR1 and SP263 (ICC ≥ 0.87 and ≥ 0.85 for TPS and CPS, respectively). QR1, SP263, and 28-8 showed the highest concordance with mRNA expression (ICC ≥ 0.81 for CPS). Accordingly, we proposed a standardized method for PD-L1 immunodetection and scoring, then tested it on 40 metastatic melanomas. This method included analysis of specimen quality (e.g., host-tumor interface and pigmentation). Concordances among antibodies were excellent for all criteria, and concordances among pathologists were better for the MELscore than for other scores.Conclusion: Harmonization of PD-L1 staining and scoring in melanomas with good concordance is achievable using the PD-L1 IHC protocols applied to other cancers; this reproducible approach can simplify daily practice. Our proposal for a PD-L1 standardized methodology has higher reproducibility across pathologists for clinical and research use.

International audience

Recurrent activating Gαq mutations in the spectrum of blue nevi have been well studied. However, the clinicopathologic characteristics of the recently described CYSLTR2-mutant and PLCB4-mutant blue nevi remain limited, owing to their rarity. Herein, we present 7 CYSLTR2-mutant melanocytic neoplasms, including 1 cellular blue nevus, 4 atypical cellular blue nevi, and 2 blue nevus-like melanomas. They occurred on the scalp, breast, flank, forearm, thigh, leg, and ankle of 3 male patients and 4 female patients, with a median age of 43 (25 to 81) years at diagnosis. Five exhibited an exophytic growth, and 6 were heavily pigmented. A fascicular arrangement of medium to large spindle melanocytes was seen in 6 cases, but epithelioid cytology was present in only 2 cases, one of them being focal. A junctional component was present in 3 cases. Immunoreactivity for HMB45 was diffusely present, except in 1 cellular blue nevus. BAP1 nuclear immunoexpression was lost in 1 melanoma case. A canonical CYSLTR2 L129Q hotspot mutation was present in all cases. Altogether, these histopathologic findings suggest that CYSLTR2-mutant melanocytic blue neoplasms frequently exhibit a heavily pigmented exophytic tumor with a silhouette resembling "pigmented epithelioid melanocytoma" rather than usual cellular blue nevus. Moreover, most of these tumors were not clinically recognized as blue nevi and not located in the classic topography of cellular blue nevus aside from the scalp. However, a fascicular arrangement of medium to large-sized spindled melanocytes, as well as a lack of epithelioid or nevoid melanocytes, could be potential diagnostic clues to morphologically distinguish CYSLTR2-mutant tumors from "pigmented epithelioid melanocytoma."

A cutaneous melanocytic tumor with morphologic overlap with clear cell sarcoma, but defined by CRTC1-TRIM11 gene fusion, was recently described in a series of five adult patients. Here, we expand the clinicopathologic features of this entity by four additional cases which include pediatric presentation, exophytic growth, and propensity to occur on the head. Patients (2F; 2M) had a median age of 41 years (range 11-59). Sites of involvement included leg, ear, and face. Tumors were circumscribed, unencapsulated, mostly limited to the dermis, and varied from 5 to 35 mm. One case was exophytic. Lesional cells were arranged in nests and fascicles, and were monomorphic and fusiform with moderate pale to clear cytoplasm, occasional nuclear pseudo-inclusions, and small to prominent nucleoli. Mitotic rate was variable (rare to 12/10 HPF, median 3/10 HPF). The pediatric case showed increased nuclear pleomorphism, tumor necrosis, and mitotic figures. All cases showed strong, diffuse nuclear staining for SOX10, but were negative or focal for S100 protein, HMB45 and Melan-A expression. Cases were positive by FISH technique and/or RNA sequencing for a TRIM11 rearrangement/fusion, and negative for EWSR1 rearrangement. This series is presented to aid in further characterization of this novel melanocytic tumor.

Background Multiple BRCA1-associated protein 1 (BAP1)-inactivated melanocytic tumors (BIMTs) have been associated with a familial cancer syndrome involving germline mutations in BAP1. Objectives We sought to describe the clinical and dermoscopic features of BIMTs. Methods This was a retrospective, multicenter, case-control study. Participating centers contributed clinical data, dermoscopic images, and histopathologic data of biopsy-proven BIMTs. We compared the dermoscopic features between BIMTs and control patients. Results The dataset consisted of 48 BIMTs from 31 patients (22 women; median age 37 years) and 80 control patients. Eleven patients had a BAP1 germline mutation. Clinically, most BIMTs presented as pink, dome-shaped papules (n = 24). Dermoscopically, we identified 5 patterns: structureless pink-to-tan with irregular eccentric dots/globules (n = 14, 29.8%); structureless pink-to-tan with peripheral vessels (n = 10, 21.3%); structureless pink-to-tan (n = 7, 14.9%); a network with raised, structureless, pink-to-tan areas (n = 7, 14.9%); and globular pattern (n = 4, 8.5%). The structureless with eccentric dots/globules pattern and network with raised structureless areas pattern were only identified in BIMT and were more common in patients with BAP1 germline mutations (P Limitations Limitations included our small sample size, retrospective design, the absence of germline genetic testing in all patients, and inclusion bias toward more atypical-looking BIMTs. Conclusions Dome-shaped papules with pink-to-tan structureless areas and peripheral irregular dots/globules or network should raise the clinical suspicion for BIMT.

e21592 Background: While 10% of melanomas occur in a context suggesting hereditary predisposition, a clear molecular explanation has only been established for approximately 20% of families. In the course of clinical care, we identified a new CTNNA1 truncating germline mutation in a family affected by multiple early-onset melanomas. Methods: NGS and CGH-array were performed on the index case’s melanoma, followed by Sanger sequencing of the germline DNA of relatives. Immunochemistry (IHC) was employed to evaluate the level of αE-catenin (encoded by CTNNA1) in the family's samples. Stable CTNNA1 knockout human melanoma cell lines were generated to investigate the functional effects of CTNNA1 loss. Functional assays, including colony formation, 3-D tumor spheroid formation, wound healing, and transwell invasion were performed, as well as electron microscopy and RNAsequencing (RNAseq). CTNNA1 mutational status was determined in several databases and further sequencing of CTNNA1 in a DNA bank of families with multiple melanomas was done. Results: While the allele frequency in the index patient’s tumoral DNA was compatible with a germline mutation, the CTNNA1 F611fs*10 mutation was subsequently found cosegregating with individuals affected by melanoma in the family. CGH array on tumor DNA identified a segmental loss on chromosome 5, leading to a loss of heterozygosity of CTNNA1, resulting in a loss of αE-catenin observed by IHC. Clinically, the mean age of first melanoma diagnosis was 29,7 years (range: 18-56), 2 were metastatic, and the others were SSM (superficial spreading melanoma) in situ (n = 3) or Breslow index 0,56 mm (n = 1). Functional assays performed on CTNNA1 KO melanoma cell lines showed a loss of cell-to-cell adhesion phenotype, in accordance with the altered adherens junctions observed by electron microscopy, and the specific pathway enrichments observed by RNAseq. This specific phenotype could be rescued by transfection with a plasmid containing wild-type CTNNA1, as opposed to the CTNNA1 F611fs* plasmid. Germline CTNNA1 mutations are rare as none could be further identified in a DNA bank of 27 multiple melanoma families. In a database of 4743 melanomas somatically sequenced for CTNNA1, 131 of them had a CTNNA1 alteration (2,76%), with a median tumor mutational burden of 44 mut/MB of DNA (range from 0 to 451). Among them, 15 alterations were predicted to be inactivating, including 7 associated with a BRAF or NRAS activating mutation. Conclusions: Altogether, our results strongly support that CTNNA1 loss of function predisposes to melanoma formation characterized by a decreased cell adhesion. Since germline CTNNA1 alterations have already been implicated in lobular breast cancers and hereditary diffuse gastric cancers, CTNNA1 likely constitutes a tumor suppressor gene involved in familial melanoma, thus broadening the spectrum of syndromes associated with this gene.

International audience; Spitz nevi are indolent melanocytic tumors arising preferentially during and after childhood. Over the last decades, recurrent oncogenic drivers, sparsely detected in melanoma, were identified in Spitz melanocytic proliferations. Therefore, the detection of such drivers appears as a relevant diagnostic tool to distinguish both entities. Interestingly, morphologic features might correlate with the oncogenic drivers. Thus, the goal of this study was to assess the performances of previously identified morphological criteria to predict the presence of specific drivers. In total, 352 Spitz melanocytic proliferations either with a genetically identified oncogenic driver or investigated for ALK, ROS1, and NTRK1 overexpression by immunohistochemistry were enrolled in the present study. The microscopic features of the cases were assessed blindly with regards to the molecular status and, performances of previously described morphological criteria to predict the molecular status were assessed applying the likelihood-ratio test (LHR). Overall, an oncogenic driver was identified in 76% of the cases (n = 268/352). No microscopic features allowed the reliable prediction of ROS1- and NTRK1-overexpressing cases. By contrast, a plexiform pattern can contribute to the recognition of ALK-overexpressing cases (LHR(+) = 6.14). Importantly, the pseudo-schwannoma variant was highly suggestive of NTRK3-rearranged cases (LHR(+) = 43). Moreover, atypical/malignant tumor (LHR(+) = 5.18), severe cellular atypia (LHR(+) = 5.07), and p16 loss (LHR(+) = 14) contribute to the recognition of MAP3K8-rearranged cases, while the presence of a sheet-like architecture (LHR(+) = 5.39) and a marked fibrosis of the stroma (LHR(+)=5.06) were predictive of BRAF-fused tumors. To conclude, our study confirms ALK-overexpressing, NTRK3-, MAP3K8-, and BRAF-rearranged cases harbored distinct morphologic features allowing their microscopic recognition.

Clear cell morphology is an uncommon finding in tumors. A subset of clear cell neoplasms also shows melanocytic differentiation, including clear cell sarcoma, PEComa, and some subtypes of renal cell carcinoma. A hallmark of these tumor types is the activation of a member of the MIT/TFE family of transcription factors, which includes MITF, TFE3, TFEB, and TFEC. Microphthalmia transcription factor (MITF is the master regulator of melanin synthesis, while TFEB plays a critical role in lysosome biogenesis. Cytogenetic translocations involving TFE3 and TFEB are now well described in multiple tumor types, but there has been little evidence to suggest similar regulation of MITF. Here we describe a series of 7 clear cell cutaneous neoplasms with melanocytic differentiation that are characterized by ACTIN-MITF gene fusions, either ACTB-MITF or ACTG1-MITF. The chromosomal breakpoints preserve MITF's dimerization and transcriptional activation domains, suggesting that these fusion proteins likely result in hyperactive MITF function, analogously to the previously reported TFE3 and TFEB fusions. Our findings indicate that MITF gene rearrangements may be key drivers of tumor pathogenesis and expand the spectrum of neoplasia associated with the MIT/TFE family.

Background: The diagnosis of dermal primary and metastatic melanocytic tumors is often problematic. Recently, a new entity has been proposed, cutaneous melanocytoma with CRTC1‐TRIM11 fusion (CMCT). Case presentation: We report the 11th case of cutaneous melanocytoma harbouring the CRTC1-TRIM11 fusion. The patient is a 35‐year‐old female patient, with no particular history, who presented in the dermatology department for a 1.5cm nodular lesion on the dorsal aspect of the left foot. The lesion evolved for more than one year. She underwent tumour resection for clinical suspicion of malignant melanoma. Pathological examination of the resected specimen after H&E stain revealed a dermal symmetrical proliferation made of spindle cells showing a melanocytic differentiation proved by expression of Melan A, S100 protein and SOX10. FISH study helped exclude a clear cell sarcoma. RNA sequencing showed the CRTC1-TRIM11 fusion.Conclusions: Since only 11 cases have been documented, and because of the overlap with the clear cell sarcoma, the characterization of CMCT is still not fully satisfactory.

The presence of melanocytic differentiation in tumors of non-melanocyte origin is uncommon and is typically associated with the overexpression of MITF, the master regulator of melanin synthesis, or another member of the MIT/TFE3 family. In clear cell sarcoma, the presence of either an EWSR1-ATF1 or EWSR1-CREB1 translocation-derived fusion protein is thought to drive melanocytic differentiation by directly stimulating the expression of MITF. Here, we describe a clear cell neoplasm with melanocytic differentiation that is characterized by a novel MITF-CREM gene fusion. CREM is the third member of the ATF1/CREB1/CREM family, and the nature of the MITF-CREM fusion appears analogous to the EWSR1-ATF1 and EWSR1-CREB1 fusions. Thus, this MITF-CREM-rearranged clear cell tumor represents a novel entity with morphologic, immunohistochemical, and molecular similarity to clear cell sarcoma.

We report a series of 6 melanocytic proliferations harboring both NRAS and IDH1 hotspot mutations. Clinically, there was no specific sex-ratio, ages ranged from 18 to 85 years, and the trunk and limbs were the most affected localizations. In half of the cases, progressive modification of a pre-existing nevus was reported. Morphologically, all tumors were predominantly based in the dermis and the most striking pathologic finding was the presence of a background architecture of congenital-type nevi with a superimposed biphasic pattern formed by dendritic pigmented melanocytes surrounding areas of nevoid melanocytes. This finding was further underscored by HMB45 staining, which was positive in the dendritic cells and negative in the nevoid melanocytes. Four cases displayed increased cellularity and 1 case showed increased dermal mitotic activity. DNA and RNA sequencing revealed NRAS and IDH1 comutations in all 6 cases, with homogenous expression data according to unsupervised clustering analysis. Array-comparative genomic hybridization revealed no copy number alteration for the 2 most cellular and mitogenic cases. All were surgically excised, available follow-up for 2 patients showed no relapse nor metastases. We hypothesize that the IDH1 mutation is a secondary event in a pre-existing NRAS-mutated nevus and could be in part responsible for the emergence of a pigmented dendritic dermal component. So far, such comutations have been reported in one benign melanocytic nevus and several melanomas. This combination could represent a new subgroup of intermediate prognosis (melanocytoma) with a distinctive morphology. Further acquisition of genomic anomalies could progressively lead to malignant transformation.

A subset of Spitz tumors harbor fusions of NTRK3 with ETV6, MYO5A, and MYH9. We evaluated a series of 22 melanocytic tumors in which an NTRK3 fusion was identified as part of the diagnostic workup. Tumors in which NTRK3 was fused to ETV6 occurred in younger patients, were predominantly composed of epithelioid melanocytes, and were classified by their histopathologic features as Spitz tumors. In contrast, those in which NTRK3 was fused to MYO5A were predominantly composed of spindled melanocytes arrayed in fascicles with neuroid features such as pseudo-Verocay bodies. To further investigate the effects of the fusion kinases ETV6-NTRK3 and MYO5A-NTRK3 in melanocytes, we expressed them in immortalized melanocytes and determined their subcellular localization by immunofluorescence. ETV6-NTRK3 was localized to the nucleus and diffusely within the cytoplasm and caused melanocytes to adopt an epithelioid cytomorphology. In contrast, MYO5A-NTRK3 appeared excluded from the nucleus of melanocytes, was localized to dendrites, and resulted in a highly dendritic cytomorphology. Our findings indicate that ETV6-NTRK3 and MYO5A-NTRK3 have distinct subcellular localizations and effects on cellular morphology.

Due to its high proclivity to metastasize, and despite the recent development of targeted and immune therapy strategies, melanoma is still the deadliest form of skin cancer. Therefore, understanding the molecular mechanisms underlying melanoma invasion remains crucial. We previously characterized Tspan8 for its ability to prompt melanoma cell detachment from their microenvironment and trigger melanoma cell invasiveness, but the signaling events by which Tspan8 regulates the invasion process still remain unknown. Here, we demonstrated that β-catenin stabilization is a molecular signal subsequent to the onset of Tspan8 expression, and that, in turn, β-catenin triggers the direct transcriptional activation of Tspan8 expression, leading to melanoma invasion. Moreover, we showed that β-catenin activation systematically correlates with a high expression of Tspan8 protein in melanoma lesions from transgenic Nras; bcat* mice, as well as in deep penetrating naevi, a type of human pre-melanoma neoplasm characterized by a combined activation of β-catenin and MAP kinase signaling. Overall, our data suggest that β-catenin and Tspan8 are part of a positive feedback loop, which sustains a high Tspan8 expression level, conferring to melanoma cells the invasive properties required for tumor progression and dissemination.

Melanocytic tumors rarely display extensive dermal myxoid deposits except in the myxoid variant of melanoma. We describe in 4 patients the unusual association of morphologic and genetic features. All cases occurred in males and were located on the limbs or proximal girdle area. Age at diagnosis ranged from 8 to 47 years. Size ranged from 6 to 11 mm. Microscopic analysis showed compound, but mainly dermal melanocytic nevi, all presenting a deep dermal expansion with fascicules of amelanotic spindled cells floating in a myxoid background. Cytologic atypia and mitotic activity were low. The superficial portion was either of spitzoid or nevoid cytology with a limited junctional component. In the initial case, the dermal myxoid component was predominant with rare, barely visible, superficial melanocytic nests. This peculiar morphology was responsible for a delayed diagnostic, which required an extensive panel of antibodies ruling out most, potentially myxoid, soft tissue tumors. We later observed the presence of similar, but more limited, dermal morphologic features in 3 other cases. Immunohistochemistry in the deep myxoid areas was melanA, ALK, SOX10, and MiTF. Molecular studies confirmed the ALK rearrangement by an ALK break-apart fluorescence in situ hybridization technique and by RNA sequencing. The latter identified 4 different 5'-fusion partners. Two gene fusions were undescribed: FBXO28(e2)-ALK(e19) and NPAS2(e2)-ALK(e19), and 2 previously described: TPM3(e7)-ALK(e20) and PPFIBP1(e9)-ALK(e19). No relapse or metastatic evolution was seen during follow-up (3 to 24 mo). We denominated this potentially challenging new variant of compound nevus linked to a kinase fusion: Melanocytic Myxoid Spindle Cell Tumor with ALK Rearrangement.

We report 5 cases of primary intradermal nodular unpigmented tumors with a melanocytic immunophenotype associated with a novel CRTC1-TRIM11 fusion. Clinically, the cutaneous nodules were slowly growing in 3 women and 2 men (25 to 82 y old, median, 28 y) with no specific topography. Lesion size ranged from 4 to 12 mm (median, 5 mm). The tumors were strictly located in the dermis with a nodular pattern. The cells were arranged in confluent nests and fascicules. Central fibronecrotic areas were present in 2 cases. Cells were medium to large, sometimes multinucleated, and presented a spindled and epithelioid cytology with prominent nucleoli. Cytonuclear atypia was constant, and mitotic activity in hotspot areas ranged from 1 to 5/mm². Immunohistochemistry found a constant positivity with S100, MiTF, and Sox10, and a heterogenous staining by MelanA or HMB45. NTRK1 was strongly positive in 3 cases. In all cases, RNA sequencing found an invariable CRTC1(e1)-TRIM11(e2) fusion, confirmed by fluorescent in situ hybridization techniques with a TRIM11 break-apart probe. In 4/4 cases, nuclear TRIM11 expression was positive by immunohistochemistry. Fluorescent in situ hybridization techniques showed no rearrangement of NTRK1 or EWSR1, and array-comparative genomic hybridization displayed no alteration (1 case) or only a whole chromosome 7 gain (2 cases) when performed. No relapse or metastatic event was observed during follow-up [3 to 72 months (median, 14 mo)]. Cutaneous clear cell sarcoma was the main differential diagnosis. Overlapping morphologic features previously described in primary dermal melanomas and paraganglioma-like melanocytic tumors were present. The CRTC1-TRIM11 fusion appears to be specific of an unpigmented nodular tumor combining a melanocytic phenotype and low-grade tumor behavior.

The current classification of melanocytic tumors includes clinical, pathological, and molecular data. A subset of lesions remains difficult to classify according to these complex multilayer schemes. We report two cases of deeply infiltrating melanomas with a sclerosing background. The first case occurred on the back of a middle-aged man appearing clinically as a dermatofibroma. The architectural and cytological aspects resembled those of a desmoplastic melanoma but the strong expression of both melanA and HMB45, two stainings usually reported as negative in this entity, raised the question of an alternate diagnosis. The second case was a large, slowly growing, perivulvar tumor in a middle-aged woman. The morphology was complex with a central junctional spitzoid pattern associating an epidermal hyperplasia with large nests of large spindled melanocytes. The dermal component was made of deeply invasive strands and nests of nevoid unpigmented melanocytes surrounded by fibrosis; a perineural invasion was present at the periphery of the lesion. In both cases, aCGH found, among many other anomalies, a chromosomal breakpoint at the BRAF locus. RNA sequencing identified in both an AKAP9-BRAF gene fusion. A complementary resection was performed and no relapses have been observed in the respectively 15 and 6 months of follow-up. Both of these melanomas remained unclassified. We further review the variety of melanocytic tumors associated with such BRAF fusions.

Resume Nous rapportons le cas d’un homme âge de 57 ans hospitalise pour la prise en charge chirurgicale d’un nodule vesiculaire fixant a la tomographie par emission de positrons. Celui-ci est decouvert fortuitement au cours du suivi d’un melanome cutane. Une cholecystectomie est effectuee. L’examen microscopique montre une infiltration de toute la paroi de la vesicule biliaire par une proliferation fortement pigmentee faite de cellules allongees aux noyaux nucleoles, anisocaryotiques avec de nombreuses mitoses atypiques. L’immunohistochimie confirme la nature melanocytaire de cette proliferation avec un marquage de l’HMB-45, de la P-S100 et du Melan-A. Devant la suspicion de metastase vesiculaire d’un melanome cutane, une etude immunohistochimique (p16, desmine et BRAFV600E) et moleculaire (sequencage du gene BRAF) complementaire est effectuee et est compatible avec une localisation secondaire. Le diagnostic de metastase vesiculaire d’un melanome est pose. Les localisations secondaires vesiculaires de melanomes sont exceptionnelles. Le but de notre travail est d’en rapporter un cas avec sa caracterisation immunohistochimique et moleculaire, d’effectuer une synthese de la revue des cas publies dans la litterature et d’envisager le principal diagnostic differentiel morphologique (le melanome primitif de la vesicule biliaire).

Melanocytic BAP1-associated intradermal tumors (MBAITs) can either be sporadic or associated with a cancer-predisposition syndrome. In this study we explored the clinical status of 136 patients in which at least one MBAIT was found. 49/136 (36%) of them gave their signed consent for an oncogenetic BAP1 blood test. 28/136 patients (20%) diagnosed with an MBAIT had other MBAITs and/or a personal or familial history of BAP1-related cancers that could clinically designate them as potential carriers of a BAP1 germline mutation. 17 of these 28 patients underwent oncogenetic testing. A deleterious mutation of BAP1 was confirmed in 12/17 cases. 4/17 cases were wild-type; all had a single MBAIT and a history of skin melanoma. A variant of unknown significance was found in one case with multiple MBAITs. Among the 12 mutated cases, multiple MBAITs were present in 10/12 cases and were the only clinical sign in 4/12 cases. The remaining 32/49 blood-tested cases with an isolated MBAIT were wild type for BAP1 in 25/32 cases or showed a variant of unknown significance in 7/32 cases. We recommend, following the diagnosis of a MBAIT, performing a BAP1 immunohistochemistry in all other cutaneous melanocytic tumors removed previously or simultaneously and all skin melanomas. This screening could help clinicians prioritize which patients would most benefit from oncogenetic testing.

// Manale El Kharbili 1, 2, 3, 4 , Clement Robert 1, 2, 3 , Tiffany Witkowski 5, 6 , Emmanuelle Danty-Berger 7 , Laetitia Barbollat-Boutrand 1, 2, 3 , Ingrid Masse 1, 2, 3 , Nicolas Gadot 8 , Arnaud de la Fouchardiere 9 , Paul C. McDonald 10 , Shoukat Dedhar 10 , Francois Le Naour 11, 12 , Francoise Degoul 5, 6 , Odile Berthier-Vergnes 1, 2, 3 1 Universite de Lyon, Lyon, France 2 Universite Lyon 1, Lyon, France 3 CNRS, UMR5534, Centre de Genetique et de Physiologie Moleculaire et Cellulaire, Villeurbanne, France 4 Current address: Department of Dermatology, University of Colorado, Aurora, Colorado, USA 5 Clermont Universite, Universite d’Auvergne, Imagerie Moleculaire et Therapie Vectorisee, Clermont-Ferrand, France 6 Inserm, U990, Clermont-Ferrand, France 7 Laboratoire CarMeN (INSERM 1060, INRA1397, INSA), Universite Lyon 1, Lyon, France 8 Universite Lyon 1, Federation de Recherche Sante Lyon-Est, ANIPATH, Faculte Laennec, Lyon, France 9 Departement de Biopathologie, Centre Leon Berard, Lyon, France 10 Department of Integrative Oncology, British Columbia Cancer Research Center, Vancouver, Canada 11 INSERM U602, Villejuif, France 12 Current address: INSERM U1193, Hopital Paul Brousse, Villejuif, France Correspondence to: Odile Berthier-Vergnes, email: odile.berthier-vergnes@univ-lyon1.fr Keywords: melanoma, matrix, integrin, tetraspanin 8, ILK Received: November 09, 2016 Accepted: January 09, 2017 Published: February 04, 2017 ABSTRACT Melanoma is well known for its propensity for lethal metastasis and resistance to most current therapies. Tumor progression and drug resistance depend to a large extent on the interplay between tumor cells and the surrounding matrix. We previously identified Tetraspanin 8 (Tspan8) as a critical mediator of melanoma invasion, whose expression is absent in healthy skin. The present study investigated whether Tspan8 may influence cell-matrix anchorage and regulate downstream molecular pathways leading to an aggressive behavior. Using silencing and ectopic expression strategies, we showed that Tspan8-mediated invasion of melanoma cells resulted from defects in cell-matrix anchorage by interacting with β1 integrins and by interfering with their clustering, without affecting their surface or global expression levels. These effects were associated with impaired phosphorylation of integrin-linked kinase (ILK) and its downstream target Akt-S473, but not FAK. Specific blockade of Akt or ILK activity strongly affected cell-matrix adhesion. Moreover, expression of a dominant-negative form of ILK reduced β 1 integrin clustering and cell-matrix adhesion. Finally, we observed a tumor-promoting effect of Tspan8 in vivo and a mutually exclusive expression pattern between Tspan8 and phosphorylated ILK in melanoma xenografts and human melanocytic lesions. Altogether, the in vitro, in vivo and in situ data highlight a novel regulatory role for Tspan8 in melanoma progression by modulating cell-matrix interactions through β1 integrin-ILK axis and establish Tspan8 as a negative regulator of ILK activity. These findings emphasize the importance of targeting Tspan8 as a means of switching from low- to firm-adhesive states, mandatory to prevent tumor dissemination.

The proliferation of cells with melanocytic lineage and a nested pattern has traditionally been regarded as a characteristic feature of a wide range of benign and malignant melanocytic proliferations. Herein, we report a series of 4 clear cell sarcomas, including 3 primary cutaneous and 1 metastatic to the skin, associated with a clear-cut intraepidermal proliferation of tumor cells representing a serious potential diagnostic pitfall. All patients were male individuals, aged from 17 to 71 years (mean: 42 y). The size of the tumors ranged from 8 to 55 mm (mean: 22.2 mm, median: 13 mm). Two tumors arose on a lower extremity and 1 each on the scalp and chest. Cutaneous metastasis developed on the limb proximal to the amputation site. Histologically, all tumors were variably circumscribed nodular or multinodular proliferations within the dermis, focally extending into the subcutis. They were composed of nests and fascicles of pale spindled and epithelioid cells with finely granular or pale cytoplasm, elongated nuclei with a single prominent nucleolus, featuring mild nuclear pleomorphism, and surrounded by delicate fibrous septa. Scattered wreath-like giant cells were present in all cases. Mitotic activity was low (mean and median: 3.5 mitoses/mm). The intraepidermal component consisted in all 4 cases of nests of tumor cells localized at the dermal-epidermal junction. Nests were well-defined and composed of spindled or epithelioid cells with irregular hyperchromatic nuclei, prominent nucleoli, and scant to moderately abundant eosinophilic to pale cytoplasm. Lentiginous proliferation of epithelioid tumor cells was coupled with focal upward migration of isolated tumor cells in a single case. By immunohistochemistry, all tumors were S100 protein, melan A, and HMB45 positive. By fluorescence in situ hybridization analysis, 3 tumors displayed rearrangements in the EWSR1 gene, whereas reverse transcriptase polymerase chain reaction confirmed EWSR1(e8)/ATF1(e4) translocation in the remaining case. In conclusion, an epidermal component in primary cutaneous clear cell sarcomas, or cutaneous metastasis of the tumor, is exceptional and represents a potential diagnostic pitfall. Careful attention to the salient morphologic features in the dermal component of the tumor, as well as confirmation of EWSR1 gene rearrangement by fluorescence in situ hybridization or reverse transcriptase polymerase chain reaction, is necessary for correct recognition of the tumor and to avoid erroneous diagnosis of a benign or malignant melanocytic proliferation.

We report a series of 21 compound blue nevi, a rare variant in the vast clinical and morphological spectrum of blue melanocytic proliferations. Clinically, they presented in young adults, with a slight female predominance. One-third were located on the dorsum of the foot. Morphologically, all cases displayed large dendritic melanocytes restricted to the deep layers of the epidermis. The compound component was central and evenly distributed. Melanocytic density ranged from scarce isolated cells to a confluent lentiginous architecture. In 12 of the 21 cases, junctional nests of small, bland, weakly pigmented melanocytes were associated. These nests became confluent in the most cellular cases. In all cases, a dermal component was immediately present underneath, mainly of cellular blue nevus-type. All cases were genetically confirmed to harbor either a GNAQ or GNA11 hotspot mutation. This study expands the morphological spectrum of blue nevi that should not be restricted to a strictly intradermal melanocytic proliferation.

International audience; We report a series of 33 skin tumors harboring a gene fusion of the MAP3K8 gene, which encodes a serine/threonine kinase. The MAP3K8 fusions were identified by RNA sequencing in 28 cases and by break-apart FISH in five cases. Cases in which fusion genes were fully characterized demonstrated a fusion of the 5' part of MAP3K8 comprising exons 1-8 in frame to one of several partner genes at the 3' end. The fusion genes invariably encoded the intact kinase domain of MAP3K8, but not the inhibitory domain at the C-terminus. In 13 (46%) of the sequenced cases, the 3' fusion partner was SVIL. Other recurrent 3' partners were DIP2C and UBL3, with additional fusion partners that occurred only in a single tumor. Clinically, the lesions appeared mainly in young adults (2-59 years of age; median = 18), most commonly involving the lower limbs (55%). Five cases were diagnosed as Spitz nevus, 13 as atypical Spitz tumor, and 15 as malignant Spitz tumor. Atypical and malignant cases more commonly occurred in younger patients. Atypical Spitz tumors and malignant Spitz tumors cases tended to show epidermal ulceration (32%), a dermal component with giant multinucleated cells (32%), and clusters of pigmented cells in the dermis (32%). Moreover, in atypical and malignant cases, a frequent inactivation of CDKN2A (21/26; 77%) was identified either by p16 immunohistochemistry, FISH, or comparative genomic hybridization. Gene expression analysis revealed that MAP3K8 expression levels were significantly elevated compared to a control group of 57 Spitz lesions harboring other known kinase fusions. Clinical follow-up revealed regional nodal involvement in two of six cases, in which sentinel lymph node biopsy was performed but no distant metastatic disease after a median follow-up time of 6 months.

International audience; A girl, born with a posterior lumbosacral giant congenital nevus, developed a central nodule that expanded over a period of 14 months into a 10-cm pedunculated mass. Histological analysis of the mass revealed melanoma of myxoid, small round-cell type with areas of rhabdomyosarcomatous transformation confirmed by immunohistochemistry. RNA sequencing identified an in-frame SASS6(e14)-RAF1(e8) fusion in both components and the nevus. A RAF1 FISH break-apart test found a balanced rearrangement pattern in the nevus and an unbalanced pattern in the malignant areas. Wild-type status of NRAS and BRAF was confirmed by NGS techniques. The array-CGH profile displayed copy number alterations commonly found in rhabdomyosarcomas. Despite intensive treatment, widespread metastatic evolution of the melanomatous component was observed.

Activating NTRK1 fusions have been described as oncogenic events across the spectrum of Spitz tumors. Herein we report a series of 38 Spitz tumors with NTRK1 fusion. These Spitz tumors have distinctive histopathologic features characterized by filigree-like rete ridges which are elongated, thin and branched, dermal melanocytes arranged in a rosette-like configuration, and marked diminishment of melanocyte size with descent into the dermis. These features are distinct from those of other genetically defined subtypes of Spitz tumors and can aid in microscopic diagnosis and help prioritize in case selection for molecular testing in the rare patients that need targeted therapy.

We report two cases of fibrous histiocytoma (FH) associated with discrete nodular aggregates of Langerhans cells (LCs) resembling Langerhans cell histiocytosis (LCH). In addition, the LCs showed positivity for BRAF V600E immunohistochemistry, a finding reported in neoplastic but not reactive LCs 1. To our knowledge, these cases represent the first published association of FH and LCH. This article is protected by copyright. All rights reserved.