Cutaneous VCL::ALK fusion ovoid‐spindle cell neoplasm

Abstract

Cutaneous VCL::ALK fusion spindle (ovoid) cell tumor is unique. Recently emerged RAS::MAP tyrosine kinase fusion sarcomas more commonly involve subcutis, skeletal muscle and even bone. We share our experience with a novel cutaneous VCL::ALK spindle cell tumor. An 11‐year‐old male presented with a back pedunculated pink–red papule thought to be a pyogenic granuloma. Biopsy histopathology revealed an epithelial collarette with pedunculated tumor extending to deep dermis/subcutis interface. 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. ALK immunostain being positive, a next‐generation sequencing comprehensive fusion panel was performed to reveal a VCL::ALK fusion. 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. Complete excision was performed with favorable follow‐up to date. 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.

CD30 expression in an emerging group of mesenchymal spindle cell neoplasms with ALK fusion detected by flow cytometry and immunohistochemistry

“…13 Interestingly, recent studies have described novel ALK-rearranged mesenchymal tumors with epithelioid morphology, including a subset of cases displaying variable mixed spindled areas. [14][15][16][17] In addition, IHC for CD30 was utilized for evaluation in two of these cases, and both tumors had CD30 expression. 14 These two tumors showed epithelioid and occasional rhabdoid cytomorphology lacking both S100 and CD34 expression, without characteristic features/fusions associated with EIMS, and behaved aggressively.…”

“…EIMS is a rare, aggressive subtype of IMT and usually displays positive staining for myoid markers, including SMA and desmin 13 . Interestingly, recent studies have described novel ALK ‐rearranged mesenchymal tumors with epithelioid morphology, including a subset of cases displaying variable mixed spindled areas 14–17 . In addition, IHC for CD30 was utilized for evaluation in two of these cases, and both tumors had CD30 expression 14 .…”