Endometrioid adenocarcinoma arising from colonic endometriosis mimicking primary colonic carcinoma.

The clinicopathologic features of a case of endometrioid adenocarcinoma arising from colonic endometriosis that clinically and histologically mimicked a primary colonic carcinoma are reported. The differential diagnostic features of the tumor leading to the correct diagnosis included associated endometriosis, a minor mucosal component, focal squamous differentiation, absence of dirty necrosis, low nuclear grade, absence of a colonic adenoma, and a CK7+/CK20-/CEA- immunophenotype.