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Case Reports

Abstract

Herein we describe a lesion in a 57-year-old man, who presented with a firm, hyperpigmented papulonodule on dorsal right hand. A shave biopsy was performed. Histopathology revealed a relatively circumscribed dermal spindle cell proliferation.The lesional cells had moderate amount of eosinophilic cytoplasm, spindled nuclei, fine chromatin and inconspicuous nucleoli with cells arranged in bundles and nests, with thick intervening collagen fibers.  No overt cytological atypia or atypical mitotic activity were identified. Immunohistochemistry was positive for SOX10 and S100 stains, and negative for CD34, p16, desmin, CK AE1/AE3, pan-Trk, BRAF V600 E, NRAS Q61R, HMB45, PRAME and Melan-A stains.  The MITF stain showed focal nuclear staining. Differential diagnosis of Cutaneous melanocytic tumor with CRTC1::TRIM11 fusion, clear-cell sarcoma and Spitz lesion, were considered. Next-generation sequencing, performed at outside laboratories using a sarcoma gene fusion panel and a 648-gene panel, revealed no gene fusions or reportable pathogenic variants, including TERT promoter mutation. These results argue against the possibility of CRTC1:TRIM 11 cutaneous tumor and clear-cell sarcoma. Combining all findings, biopsy was signed out as “SOX10 and S100 positive spindle cell neoplasm” with possibility of Spitz melanocytoma (atypical Spitz tumor) or another cutaneous spindle cell neoplasm with melanocytic differentiation. The patient is scheduled to undergo excision. This case describes a diagnostically challenging cutaneous spindle cell neoplasm, with aberrant immunohistochemical expression, even after expert consultation, exhausting immunohistochemical and molecular workup. This novel case could expand spectrum of tumors in lineage of “SOX10+S100+ spindle cell neoplasm”.