Collision in the colon: concurrent adenocarcinoma and diffuse large B-cell lymphoma in the same tumour.

Double malignancies in the gastrointestinal tract are unusual. Concurrent lymphoma and adenocarcinoma is a rare clinical condition. We herein report a collision tumour which first presented with a diffuse large B-cell lymphoma in the skull base and ileocecal junction area. After rituximab and chemotherapy the skull base tumour disappeared, but the ileocecal lesion remained. A biopsy revealed the presence of adenocarcinoma in the same lesion. The tumour was surgically removed. Further microscopic examination of the tumour showed it was an adenocarcinoma but residual lymphoma cell infiltration could still be observed. Serum Epstein-Barr virus (EBV) was detected at diagnosis of lymphoma and the concentration further elevated at diagnosis of adenocarcinoma. Therefore, both lymphoma and carcinoma may be EBV related. Our experience illustrated that such collision tumours are rare and difficult in diagnosis. Clinicians and pathologists should be aware of such an association in order to make a correct diagnosis and initiate proper treatment.