A new case of cutaneous melanocytoma harbouring the CRTC1‐TRIM11 fusion: case report

Abstract Background: The diagnosis of dermal primary and metastatic melanocytic tumors is often problematic. Recently, a new entity has been proposed, cutaneous melanocytoma with CRTC1‐TRIM11 fusion (CMCT). Case presentation: We report the 11th case of cutaneous melanocytoma harbouring the CRTC1-TRIM11 fusion. The patient is a 35‐year‐old female patient, with no particular history, who presented in the dermatology department for a 1.5cm nodular lesion on the dorsal aspect of the left foot. The lesion evolved for more than one year. She underwent tumour resection for clinical suspicion of malignant melanoma. Pathological examination of the resected specimen after H&E stain revealed a dermal symmetrical proliferation made of spindle cells showing a melanocytic differentiation proved by expression of Melan A, S100 protein and SOX10. FISH study helped exclude a clear cell sarcoma. RNA sequencing showed the CRTC1-TRIM11 fusion.Conclusions: Since only 11 cases have been documented, and because of the overlap with the clear cell sarcoma, the characterization of CMCT is still not fully satisfactory.