LAUSR

Desmoid fibromatosis is a myofibroblastic neoplasm of intermediate biologic potential, which has a strong predilection for local recurrence but does not metastasize. Arranged in long, sweeping fascicles with infiltrative borders, desmoid fibromatosis typically consists of uniform, bland myofibroblastic spindle cells that harbor mutation of CTNNB1 (or less often APC). In this report, we present a remarkable case of desmoid fibromatosis associated with striking nuclear pleomorphism. We hypothesize that this striking pleomorphism is due to a germline TP53 mutation, a finding first suspected due to strong and diffuse p53 staining by immunohistochemistry and subsequently confirmed by molecular testing. The combination of the pleomorphism and TP53 mutation in desmoid fibromatosis represents a novel finding unreported in the literature.