Malignant rhabdoid tumor of the colon: report of a case.

A malignant rhabdoid tumor of the colon is very rare and only three cases have been previously described. A 76-year-old man was admitted to the hospital complaining of epigastralgia. An elastic mass was palpable in the right upper abdomen. A barium enema and endoscopic examination showed a giant gyrate tumor arising from the cecum. Abdominal ultrasonography and a computed tomography scan revealed the tumor to be located in the colon associated with multiple liver metastases and gallbladder stones. A right colectomy and cholecystectomy were thus performed. The tumor was histologically composed of sheets of large round and polygonal nuclei with vesicular chromatin, and abundant acidophilic cytoplasm, often containing hyalin-like inclusion. The cytoplasm was positive for vimentin and neuron-specific enolase, and hyaline globules of the rhabdoid tumor cells stained positive for cytokeratin in some cells. Transmission electron microscopy showed characteristic rhabdoid cells with an aggregation of intermediate filaments. A histologic diagnosis of malignant rhabdoid tumor of the colon was made. The tumor demonstrated several unusual findings for malignant rhabdoid tumors including diploidy by a flow cytometric analysis, and positive nuclear immunohistochemical staining for p53 protein and Ki-67 antigen. We report herein the third known case of a pure colonic rhabdoid tumor.