Distinct genomic features in a retrospective cohort of mucosal, acral, and vulvovaginal melanomas.

BACKGROUND: Compared with sun-exposed melanomas, less is known regarding the pathogenesis of sun-protected melanomas. Sun-protected melanomas share many epidemiologic factors, but their genetic heterogeneity is not well studied. OBJECTIVE: We investigated the genomic profile of acral, mucosal, and vulvovaginal melanomas. We hypothesize that mucosal melanomas, recognized for their uniquely aggressive clinical behavior, have distinct genomic features. METHODS: We performed whole transcriptome messenger RNA and DNA (1711 genes) sequencing, messenger RNA expression profiling, tumor mutational burden, ultraviolet signature, and copy number variants analysis on 29 volar/digital acral, 7 mucosal, and 6 vulvovaginal melanomas. RESULTS: There was significant genetic heterogeneity, particularly in acral melanomas, with 36% having BRAF alterations, whereas other melanomas had none (P = .0159). Nonzero ultraviolet signatures were more frequent in acral melanomas, suggesting greater ultraviolet involvement. Mucosal melanomas formed a distinct group with increased expression of cell cycle and proliferation genes. Various targetable aberrations were identified, such as AURKA and ERBB2, in mucosal and acral melanomas, respectively. LIMITATIONS: The sample size was a small. CONCLUSION: There is significant genetic heterogeneity among sun-protected melanomas. Mucosal melanomas have upregulation in cell cycle and proliferation genes, which may explain their aggressive behavior. Ultraviolet radiation plays some role in a subset of acral but not other melanomas.

Retrospective Cohort: Genomic Differences Between Pigmented Spindle Cell Nevi of Reed and Reed-Like Melanomas.

BACKGROUND: Some melanomas closely resemble pigmented spindle cell nevi (PSCN) of Reed histologically. The distinction of these entities is important for clinical management. A recent study showed most PSCN (78%) are fusion-driven, commonly involving NTRK3 (57%). Conversely, BRAF V600E mutations are not characteristic of PSCN but are frequent in melanoma. OBJECTIVE: In this study, we assessed clinical, histologic and genomic differences between PSCN of Reed and Reed-like melanomas (RLMs). METHODS: We performed BRAF V600E immunohistochemistry (IHC) for 18 PSCN and 20 RLM cases. All 23 benign PSCN cases previously underwent whole transcriptome and targeted DNA sequencing with a 1711 gene panel. RESULTS: We previously demonstrated the majority of PSCN (18 of 23) has chimeric fusions. Among PSCN without a chimeric fusion, BRAF mutations were common. Noncanonical BRAF mutations were identified in 2 of 5 nonfusion cases, and 1 case had a canonical BRAF mutation. Alternatively, 70% of RLM demonstrated a BRAF V600E mutation. RLM also occurred more frequently in older patients. LIMITATIONS: The overall sample size was small. CONCLUSIONS: In diagnostically challenging cases, ancillary IHC studies can assist in distinguishing PSCN from RLM. Our study suggests positive staining by IHC for BRAF V600E and older age strongly favors a diagnosis of RLM.

The role of TERT promoter mutations in differentiating recurrent nevi from recurrent melanomas: A retrospective, case-control study.

BACKGROUND: Repigmentation at previous biopsy sites pose a significant diagnostic dilemma given clinical and histologic similarities between recurrent nevi and locally recurrent melanoma. Though common in melanoma, the role of TERT promoter mutations (TPMs) in recurrent nevi is unknown. OBJECTIVE: We investigated the role of TPMs in recurrent nevi and whether the presence of hotspot TPM distinguishes recurrent nevi from locally recurrent melanoma. We also characterized clinical and histologic features differentiating these lesions. METHODS: We analyzed 11 locally recurrent melanomas, 17 recurrent nevi, and melanoma and nevus controls to determine TPM status. We also assessed clinical and histologic features of the recurrent groups. RESULTS: Hotspot TPMs were more common in recurrent melanomas than recurrent nevi (P = .008). Recurrent melanomas were more likely to have solar elastosis (P = .0047), multilayering of melanocytes in the epidermis (P = .0221), adnexal involvement (P = .0069), and epidermal consumption (P = .0204). Recurrent nevi had intra-epidermal atypia limited to the area above the scar (P < .0001) and occurred earlier after the original biopsy (P < .0008). Solar elastosis, months to recurrence, and hotspot TPMs were independently associated with recurrent melanoma in multivariate analysis. LIMITATIONS: This was a retrospective study. CONCLUSION: Hotspot TPMs are significantly more frequent in recurrent melanomas and could serve as a diagnostic clue in histologically ambiguous cases.

Histomorphologic spectrum of germline-related and sporadic BAP1-inactivated melanocytic tumors.

BACKGROUND: BRCA1-associated protein 1 (BAP1)-inactivated melanocytic tumors (BIMTs) are often the earliest sign of the BAP1 tumor predisposition syndrome. Identification of BIMTs and selection of patients for germline testing affect the lives of patients with germline BAP1 mutations. OBJECTIVE: To describe the spectrum of histomorphologic findings in BAP1-inactivated melanocytic lesions to improve their recognition. We determined the frequency of sporadic versus germline cases in our cohort, assessing whether any features were statistically linked to germline status. METHODS: Histomorphologic features of BAP1-inactivated melanocytic lesions were analyzed by comparing cases with germline mutations with those with unknown or negative status. Available clinical follow-up data were reported. RESULTS: The histomorphologic spectrum of BAP1-inactivated melanocytic lesions is broad; it includes cases with spitzoid cytomorphology (69%), smaller epithelioid cells without spitzoid features (31%), and rhabdoid cytologic features (58%). BIMTs from patients with germline mutations were statistically more likely to have an extensive junctional component of BAP1-inactivated melanocytes (P = .0177). All 11 patients with suspected or confirmed germline mutations had a history of cutaneous melanoma or multiple BIMTs. LIMITATIONS: The unknown germline status of 77 patients. CONCLUSION: Approximately 12% of patients with BIMTs have germline mutations. Extensive junctional involvement in a BIMT and a personal history of melanoma or previous BIMT may be additional indications for germline testing.

Distinct Patterns of Acral Melanoma Based on Site and Relative Sun Exposure.

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.

The diagnostic value and histologic correlate of distinct patterns of shiny white streaks for the diagnosis of melanoma: A retrospective, case-control study.

BACKGROUND: Shiny white streaks (SWSs) are best visualized with polarized dermoscopy and correlate with dermal fibroplasia histopathologically. SWSs have been described at higher frequencies in melanomas than in benign nevi. OBJECTIVE: We assessed the diagnostic value of different patterns of SWSs and their histologic correlate in melanocytic lesions. METHODS: Polarized dermoscopic images of 1507 histopathologically diagnosed melanocytic neoplasms were analyzed for presence and pattern of SWSs. Histology was also reviewed for correlation. RESULTS: Among 1507 melanocytic neoplasms, SWSs were observed in 31 of 144 melanomas (22%) and 22 of 1363 benign neoplasms (1.6%) (P < .001). The sensitivity and specificity of SWSs for melanoma were 22% and 98%, respectively. Diffuse SWSs exhibited the greatest diagnostic value for melanoma, with sensitivity of 11.8% and specificity of 99.5%. Focal central and peripheral SWSs were comparable in diagnostic significance. The presence of SWSs was highly uncommon in dysplastic nevi, whereas in certain benign subgroups of nevi such as Spitz nevi and atypical genital special site nevi, SWSs were not uncommon. Diffuse SWSs correlated with greater breadth of deep fibroplasia than focal SWSs (P = .009), and SWSs correlated with greater Breslow depth among melanomas (P = .007). LIMITATIONS: This study was retrospective. CONCLUSION: Polarized dermoscopy is a valuable diagnostic tool in the identification of SWSs, a feature that is highly specific for melanoma.