Primary B-cell mucosa-associated lymphoid tissue lymphoma presenting as a solitary colorectal polyp.

We describe two patients with low-grade and one patient with mixed low- and high-grade B-cell lymphoma of mucosa associated lymphoid tissue (MALT) type arising in the large intestine. In each patient the lesion occurred as a single polyp. Two patients presented with rectal bleeding and in one the lesion was discovered incidentally. The bone marrow was uninvolved in all three cases but in the patient with mixed low- and high-grade lymphoma involvement of mesenteric lymph nodes and liver was found. CT scan revealed no lymphadenopathy or splenomegaly in any of the patients. Two patients remain well 9 and 24 months respectively after polypectomy whereas the patient with mixed low- and high-grade lymphoma died 7 days after hemicolectomy due to cardiac failure. These previously undescribed solitary polypoid MALT lymphomas can closely resemble both benign lymphoid polyposis of the colon and lymphomatous polyposis (mantle cell lymphoma). Because of their different behaviour accurate diagnosis of polypoid MALT lymphoma is important.