[Primary diffuse large B-cell lymphoma of the rectum simulating a rectal adenocarcinoma].

Colorectal lymphoma is an extremely infrequent entity, representing less than 0.5% of all primary colorectal neoplasms. Colorectal localization accounts for 15-20% of all gastrointestinal lymphomas, after the stomach and small intestine. Because the symptoms are non-specific, this disease is usually diagnosed in the advanced stages. Dawson's criteria are highly useful in the differential diagnosis between primary colorectal involvement and gastrointestinal tract involvement secondary to systemic lymphoma, which is important due to the distinct prognosis and treatment of these entities. We report the case of a B-cell non-Hodgkin's lymphoma that was difficult to diagnose and was treated with R-CHOP polychemotherapy. Outcome was poor.