A case of diffuse large B-cell lymphoma transformed from primary duodenal follicular lymphoma.

Primary intestinal follicular lymphoma (FL) is a variant of FL characterized by frequent duodenal involvement and a very indolent clinical behavior without therapy. Unlike nodal FL, there have been no reports of histologic transformation (HT) or death attributable to primary intestinal FL. Here, we report the first case of primary duodenal FL showing HT. A Grade 1 FL in the duodenum was incidentally detected in a 73-year-old man. A watch-and-wait strategy was adopted because the disease was stage IE. Six months later, bone marrow involvement was suspected. The intestinal lesions had not changed during the first year since the initial diagnosis. Sixty-two months after the initial diagnosis, a biopsy specimen showed diffuse large B-cell lymphoma (DLBCL). A perforation of the intestine occurred before chemotherapy was started. Partial resection was performed and subsequent chemotherapy was administered. The clone of the initial FL and DLBCL were identical according to PCR analysis, indicating that the primary intestinal FL had transformed into DLBCL. Although HT is rare, it could occur in some patients with primary intestinal FL. Based on this case, it may be necessary to re-evaluate the clinical watch-and-wait strategy for primary intestinal FL in some patients.