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.

No abstract

In most cases of cutaneous melanoma, ultraviolet (UV) radiation is recognized as a prominent risk factor. Less is known regarding the mechanisms of mutagenesis for melanoma arising in sun-protected sites, such as acral and mucosal melanoma. Acral and mucosal melanoma share many common features, including a late age of onset, a broad radial growth phase with prominent lentiginous growth, the presence of field cancerization cells, and, in most cases, lack of a precursor nevus. In addition to early chromosomal instability, many of the same genes are also involved in these two distinct melanoma subtypes. To better understand non-UV-mediated pathogenesis in melanoma, we conducted a joint literature review of clinical, histological, and molecular features in acral and mucosal melanoma. We also reviewed the current literature regarding aberrations in KIT, PDGFRA, TERT, and other commonly involved genes. By comparing common features of these two subtypes, we suggest potential mechanisms underlying acral and/or mucosal melanoma and offer direction for future investigations.

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 natural history of atypical Spitz neoplasms remains poorly understood, resulting in significant patient and clinician anxiety. We sought to better characterize outcomes that correlated with molecular features by performing a prospective cohort study of pediatric atypical spitzoid neoplasms in which fluorescence in situ hybridization studies were obtained for diagnosis. Cases with sufficient tissue underwent additional retrospective assessment for translocations in ALK, NTRK1, BRAF, RET, and ROS1. Among 246 total patients assessed, 13% had a positive fluorescence in situ hybridization result. Follow-up data was available in 85 patients. Two patients had a recurrence of whom 1 had distant metastasis. Both patients had homozygous deletions in 9p21. Homozygous deletions in 9p21 significantly correlated with recurrence of disease (P = 0.027). Fifteen (36%) of 42 cases were found to have a kinase fusion protein. However, the presence of kinase fusions was nonprognostic of recurrence (P > 0.99). This study was limited by the availability and length of follow-up data and the number of adverse outcomes. The majority of atypical spitzoid neoplasms in childhood have indolent behavior. Although the subgroup of patients with homozygous deletions in 9p21 is at higher risk for aggressive clinical behavior, their prognosis seems considerably better than similarly staged conventional melanoma.