Ileocecal collision tumor composed of adenocarcinoma and primary malignant lymphoma.

Collision tumor means that two kinds of histologically distinct tumors coexist and neighbor without histological interminglement. This report describes a rare case of an ileocecal collision tumor composed of adenocarcinoma and primary malignant lymphoma. A 76-year-old woman was referred to our institute with anemia and a right lower quadrant mass. Colonoscopy revealed type 2 advanced colon cancer in the cecum accompanied by a submucosal mound neighboring this cancer, which appeared different from the usual shape of colon cancer. A barium enema study manifested the typical apple-core sign in the cecum with a smooth semicircular line appearing in the shadow of the apple-core sign. Biopsy specimens showed adenocarcinoma, so a right hemicolectomy was performed. The gross resected specimen presented a mass measuring 64 × 58 × 28 mm at the ileocecal portion. The half of this mass on the colonic side had a crater-like appearance, whereas the remaining part of the mass on the ileal side had an aspect with a smooth surface. Microscopic examination disclosed that the mass was composed of adenocarcinoma and malignant lymphoma bordering on each other and mediated by a thin layer of connective tissue. Cases of colon tumors with an unusual epithelial and submucosal appearance may be instances of collision tumors composed of cancer and malignant lymphoma.