#00065073

A 75-year-old woman presented to the office for follow-up of a recently diagnosed microsatellite instability-high (MSI-H) T3N1 gastric adenocarcinoma status-post partial gastrectomy. Upper gastrointestinal endoscopy revealed a 20 mm sessile polyp/mass in the gastric antrum (A) that was resected and sent to pathology for evaluation. Hematoxylin and eosin stain of the polypoid gastric mass demonstrated large lymphoid aggregates in a predominantly follicular pattern with closely packed and back-to-back follicles with attenuated or absent mantle zones (B, 2X). Follicle polarization and tingible-body macrophages were absent. The follicles were composed of small mainly cleaved lymphocytes (centrocytes) and scattered centroblasts (C, 20X). The number of the centroblasts per high power field was 6-15. Immunohistochemistry demonstrated that the atypical follicular lymphoid cells were positive for CD20 (D, 4X), CD10 (E, 4X), Bcl-2 (F, 4X), Bcl-6, and negative for cyclin D1. CD21 highlighted follicular dendritic cell meshwork and CD3 highlighted scattered small T-lymphocytes. Ki-67 was 20-30% in the neoplastic cells. Overall, the histomorphology and immunophenotype were compatible with follicular lymphoma, follicular pattern, low grade (1-2 of 3). No carcinoma was identified histomorphologically. Additional abdominal CT scan showed no lymphadenopathy. Extra-nodal marginal zone lymphoma (MALT-lymphoma) and large B cell lymphoma are commonly seen in gastric biopsy, however a low-grade follicular lymphoma is rarely seen, especially when it occurred as a polypoid lesion.