8/20/2023 0 Comments Spindle cells![]() This novel VCL::ALK fusion spindle (ovoid) cell tumor of the dermis is best considered as part of the recently emerged RAS::MAP tyrosine kinase fusion sarcomas.Īfter identification of classic NTRK fusions in infantile fibrosarcoma and mesoblastic nephroma, additional low- and high-grade-appearing fusion sarcomas have now been recognized in other genes of the tyrosine kinase RAS::MAPK pathway, including fusions involving NTRK1-3, BRAF, RAF1, RET, FGFR1, ABL1, and ALK. Complete excision was performed with favorable follow-up to date. While epithelioid fibrous histiocytoma shares this fusion and similar dermal location and collarette pedunculation, this and other entities were excluded by older patient age, deeper dermal involvement, ovoid-to-spindled morphology, central pericytoid vasculature, myxoid stroma, moderate cellularity with low to moderate MIB1 expression, superficial ulceration, and focal S100 protein expression. ALK immunostain being positive, a next-generation sequencing comprehensive fusion panel was performed to reveal a VCL::ALK fusion. The combination of spindled and epithelioid cells, an ovoid myopericytoid appearance within myxoid to collagenous stroma, low to moderate MIB1 and focal S100 protein without SOX10 immunostaining, were suggestive of a novel RAS::MAPK tyrosine kinase fusion sarcoma that is well described. Biopsy histopathology revealed an epithelial collarette with pedunculated tumor extending to deep dermis/subcutis interface. An 11-year-old male presented with a back pedunculated pink–red papule thought to be a pyogenic granuloma. We share our experience with a novel cutaneous VCL::ALK spindle cell tumor. Recently emerged RAS::MAP tyrosine kinase fusion sarcomas more commonly involve subcutis, skeletal muscle and even bone. Cutaneous VCL::ALK fusion spindle (ovoid) cell tumor is unique.
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