Recent studies have identified translocations involving the kinase domains of ALK, NTRK1, BRAF, RET, and ROS in spitzoid neoplasms. Subsequent studies have also characterized morphologic features corresponding to ALK and NTRK1 translocations. In this study, we sought to further compare morphologic features across a range of 49 genetically defined spitzoid neoplasms with ALK, NTRK1, BRAF, or RET fusions to determine discriminating features. We also compared them with a group of 22 spitzoid neoplasms, which were confirmed to be negative for fusions in ALK, NTRK1, BRAF, and RET. Features with the highest discriminatory value included diameter of the lesion, dermal architecture, and certain cytomorphologic features. Specifically, cases with a large diameter (≥9 mm) and wedge-shaped, plexiform dermal architecture of nests of large, spindle-shaped cells were most likely to have an ALK fusion. NTRK1-fused cases were most likely of the fusions to have Kamino bodies and were typically arranged in smaller nests with smaller predominantly spindle-shaped cells, occasionally forming rosettes. BRAF fusion cases were the only fusion subtype to have a predominance of epithelioid cells, were less organized in nests, and commonly had a sheet-like growth pattern or dysplastic Spitz architecture. BRAF fusion cases were most likely to have high-grade nuclear atypia, to be diagnosed as spitzoid melanoma, to have a positive result by melanoma fluorescence in situ hybridization assay, and to develop copy number gains in the kinase domain of the fusion protein. On the basis of experience from this cohort, BRAF-fused cases appear most likely to progress to melanoma.

IMPORTANCE Patients with germline mutations in BAP1 may develop several flesh-colored melanocytic BAP1-mutated atypical intradermal tumors (MBAITs). These tumors generally develop earlier than other BAP1-associated tumors, highlighting an important role for dermatologists in identifying and screening patients with a history suggestive of a germline mutation.OBJECTIVE To describe 8 new families with germline mutations in BAP1 and provide a comprehensive review of reported cases. DESIGN, SETTINGS AND PARTICIPANTSPatients were identified in an outpatient dermatology clinical setting over a 6-month period (10 mutation carriers from 8 families) and through a literature review using PubMed (205 patients).EXPOSURES Mutations were identified through next-generation sequencing of saliva or blood samples, and RNA was extracted from fibroblasts cultured from a patient with an intronic variant to determine the impact of the mutation on the coding sequence. MAIN OUTCOMES AND MEASURESAll 215 patients were assessed for personal and/or family history and genotype. These findings were compiled and assessed for any association between genotype and phenotype.RESULTS Overall, this study included 215 patients (108 women, 91 men, and 16 gender unspecified; median [range] age, 46.5 [10.0-79.0] years). Nine of the 10 patients who were identified in the outpatient dermatology setting were found to have MBAITs on clinical examination. Forty of 53 patients (75%) identified in the literature review who underwent total-body skin examinations (TBSE) were found to have MBAITs, suggesting a high penetrance in patients who have undergone TBSE. The most prevalent malignancies among BAP1 mutation carriers were uveal melanoma (n = 60 [28%]), mesothelioma (n = 48 [22%]), cutaneous melanoma (n = 38 [18%]), and renal cell carcinoma (n = 20 [9%]). A total of 71 unique mutations in BAP1 have been reported. CONCLUSIONS AND RELEVANCEOur results indicate that germline mutations in both coding and noncoding regions throughout the BAP1 gene can impair protein function, leading to an increased risk for several associated malignancies. Four of the 8 probands we present had no history of BAP1-associated malignancies and were assessed for germline mutations when found to have MBAITs on dermatologic examination. Dermatologists can identify patients with a high likelihood of the BAP1 cancer syndrome through personal and family history and TBSE for the presence of possible MBAITs.

Acral melanoma is distinct from melanoma of other cutaneous sites, yet there is considerable variation within this category. To better define this variation, we assessed melanomas occurring on dorsal (n = 21), volar (n = 9), and subungual/interdigital (n = 13) acral skin as well as acral nevi (n = 24) for clinical, histologic, and molecular features. Melanomas on dorsal acral surfaces demonstrated clear differences compared with volar and subungual/interdigital melanomas. The latter two groups exhibited significantly less frequent BRAF mutations (P = 0.01), were significantly less likely to have the superficial spreading histologic subtype (P = 0.01), occurred in older patients (P = 0.05), and had more frequent involvement in non-Caucasians (P = 0.01). These differences can be explained by differing levels of UV exposure. Subungual/interdigital melanomas had the most diverse group of oncogenic mutations including PIK3CA (2/13), STK11 (2/13), EGFR (1/13), FGFR3 (1/13), and PTPN11 (1/13). In addition, subungual/interdigital melanomas had a significantly higher frequency of copy number aberrations (67%) than other subgroups (P = 0.02), particularly in CDK4 and cyclin D1, and were less likely to have BRAF mutations or a superficial spreading histologic subtype (P = 0.05) compared with volar acral melanomas. Although based on a limited sample size, differences between volar and subungual/interdigital melanomas in our study may be the result of differing levels of UV exposure.

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.

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