Anterior rectal wall gastrointestinal stromal tumor presenting clinically as prostatic mass

Gastrointestinal stromal tumors (GIST) of the anterior rectal wall can present as a prostatic mass, with concomitant obstructive symptoms. Transrectal biopsies of GIST may be misdiagnosed as primary prostatic sarcomas. We report 3 cases of GIST that were initially characterized as prostatic leiomyosarcomas and treated definitively with pelvic exenteration. The correct diagnosis was possible only after immunohistochemical staining for CD117 and was made retrospectively in 2 of 3 cases. Additional therapy with imatinib (Gleevec, Novartis Pharmaceuticals Corporation, East Hanover, NJ), an inhibitor of CD117 tyrosine kinase activity, treated recurrence in one patient and effected complete remission.