Malignant lymphoid polyp - a new category of disease in the large intestine.

The gastrointestinal (GI) tract is a common site of presentation of extranodal lymphomas, although primary GI lymphomas account for only 5% to 10% of primary GI neoplasms. The majority of cases occur in the stomach; only approximately 10% occur in the colorectum. Diffuse large B-cell lymphoma is the most common type of GI tract lymphoma [1]. An asymptomatic 55-year-old man was referred for endoscopic colorectal cancer screening. A reddish polyp, measuring 1cm in largest diameter, was removed from the sigmoid colon (●" Fig.1). Histologic examination disclosed closely packed, poorly defined neoplastic follicles with attenuated or absent mantle zones (●" Fig.2a), which were composed of centrocytes and occasional centroblasts (●" Fig.2b). The neoplastic cells were positive for CD20, BCL2, and CD10 (●" Fig.3a, ●" Fig.3b, ●" Fig.3c) but lacked expression of CD5, cyclin D1, and CD30. The Ki67 labeling index was less than 10% (●" Fig.3d). The final diagnosis was follicular lymphoma (grade 1). The result of computed tomography was negative for more advanced disease, and the result of a bone marrow biopsy was also normal. Within the GI tract, follicular lymphomas appear mainly as multiple small polyps in the second portion of the duodenum, but theymay rarely also be seen in other parts of the GI tract, including the colorectum, often as an incidental finding [1,2]. Only four cases of follicular lymphoma presenting as an isolated colonic polyp have been reported [3–6]. The differential diagnosis includes mainly reactive – that is, nonneoplastic – lymphoid hyperplasia or polyp, which is most often observed in the ileum and occasionally the colon. When occurring within the rectum, reactive lymphoid hyperplasia has been referred to as rectal tonsil [7]. Primary malignant GI tract lymphoma presenting as an isolated colonic polyp is exceedingly rare. We suggest the term malignant lymphoid polyp to better categorize this lesion, which may be encountered during screening colonoscopy. Use of the term will improve differentiation of the lesion from reactive lymphoid hyperplasia, which in the GI tract is commonly referred to as benign lymphoid polyp.