CTNNB1 and desmoid tumor: A review of a core biopsy from the right lower quadrant mass confirmed desmoid-type fibromatosis, showing diffuse nuclear β-catenin, “double-rail” smooth-muscle-actin and vimentin positivity, focal factor XIIIa staining, Ki-67 < 1%, and a pathogenic CTNNB1 p.T41A mutation, with desmin, S-100, cytokeratin AE1/AE3, and CD34 all negative.