Cutaneous Melanocytic Tumor With CRTC1::TRIM11 Fusion: A Case Report.

Cutaneous melanocytic tumor with CRTC1::TRIM11 fusion (CMTCT) is a rare and recently recognized melanocytic neoplasm with fewer than 50 reported cases. These tumors can be diagnostically challenging due to overlapping histologic features with malignant melanoma and clear cell sarcoma (CCS). This report adds to the limited literature by describing a 50-year-old male with an atypical inflamed cystic lesion on the shin. Biopsy revealed a dermal proliferation of atypical epithelioid cells within a desmoplastic stroma. Immunohistochemistry was positive for SRY-box transcription factor 10 (SOX-10) and microphthalmia-associated transcription factor (MITF), confirming melanocytic differentiation. Due to morphologic overlap with CCS, the specimen was referred for advanced molecular analysis, which confirmed a CRTC1::TRIM11 fusion. The lesion was completely excised, and the patient underwent close dermatologic surveillance and follow-up. This case adds to the recognized clinical spectrum of CMTCT. We highlight the diagnostic complexity and role of molecular testing in distinguishing CMTCT from more common and aggressive neoplasms. Increased awareness among dermatologists and dermatopathologists can promote timely recognition and accurate diagnosis. The goal is for the expanding body of knowledge on CMTCT to continue informing diagnosis, long-term management, and providing insight into prognosis.