ABSTRACT
Malignant rhabdoid tumors were first described in 1978 by Beckwith and Palmer as a rare variant of Wilms' tumors with a "rhabdomyosarcomatoid" pattern and a particularly poor prognosis. Week reclassified this disease as a distinct disease in 1989 and thereafter, there have been several reports about malignant rhabdoid tumor that occurred in various organs, including the colon. The histologic characteristics of rhabdoid tumor are noncohesive or loosely cohesive cells with high cellularity, an eccentric large nucleus and eosinophilic cytoplasm, and the cytoplasm is usually positive for vimentin and it contain hyaline inclusions. On immunohistochemical staining, the cells are usually positive for vimentin and cytokeratin and they are negative for desmin. This tumor progresses rapidly and it has a very poor prognosis, but survival is better if there is no lymphatic or distant metastasis. We experienced a patient who suffered with undifferentiated adenocarcinoma with rhabdoid features in the ascending colon.