OGT-rearranged mesenchymal neoplasm of the palm with a novel C3orf62/MAPS partner gene: expanding the molecular spectrum of this rare entity.

OGT-rearranged mesenchymal neoplasm is a rare, molecularly defined soft tissue tumor with an acral predilection and recurrent fusions involving FOXO1, FOXO3, FOXO4, or CITED1. We report a tumor of the left ulnar palm in a 72-year-old woman presenting as a scaly papule. Shave biopsy demonstrated a bland dermal mesenchymal neoplasm composed of epithelioid to spindled cells arranged in cords and small nests within a hyalinized to fibromyxoid stroma. The lesional cells expressed CD34 diffusely and EMA focally, whereas SOX10 and SMA were negative. Targeted RNA sequencing identified a novel in-frame OGT::C3orf62/MAPS fusion joining OGT exon 22 to MAPS exon 3 and predicted to preserve the OGT enzymatic architecture. MAPS is implicated in phase separation and chromatin organization. This case expands the molecular and clinical spectrum of OGT-rearranged mesenchymal neoplasm, documents C3orf62/MAPS as a novel fusion partner, and highlights its dermal papular presentation as a potential diagnostic pitfall in routine dermatopathology.