Prominent Mott cell proliferation in Epstein-Barr virus-associated gastric carcinoma.

The proliferation of Mott cells (plasma cells with multiple Russell bodies) is rarely observed in nonhematopoietic tumors, and no reports of this phenomenon in malignant epithelial neoplasms have been published. We present 2 cases of gastric carcinoma associated with prominent Mott cell proliferation. Histologically, both tumors consisted of extensive lymphoplasmacytic infiltration and numerous Mott cells with dysplastic epithelial cells. The epithelial cells showed overt cytologic atypia; infiltrating cells did not show cytologic atypia, immunoglobulin light chain restriction, or clonal immunoglobulin gene rearrangement. In situ hybridization for Epstein-Barr virus (EBV)-encoded small RNA (EBER) labeled the carcinoma cells but not the lymphoplasmacytic cells. The Mott cell accumulation was a reactive phenomenon in gastric carcinoma associated with EBV. The differential diagnosis included primary gastric lymphoma and nonneoplastic conditions such as Russell body gastritis; EBER in situ hybridization was helpful in their differentiation.