Primary gastric plasmacytoma: a morphological and immunohistochemical study of five cases.

Five cases of primary gastric plasmacytoma were studied histopathologically and immunohistochemically. Plasmacytoid cells proliferated diffusely in the propria mucosa, almost preserving the structure of gastric glands. Occasionally, intranuclear inclusions, giant cells, and needle-shaped crystalline inclusions were observed. The neoplastic nature could be suspected on the basis of these histological findings. Immunohistochemically, three cases were positive for IgM and two for IgA. IgM positivity was more commonly observed in the gastric plasmacytoma than in multiple myeloma. Another immunohistochemical study demonstrated that LN-1 negativity and anti-EMA antibody positivity might be an indicator to differentiate gastric plasmacytoma from other types of gastric lymphoma. Four cases of early-stage gastric plasmacytoma have been followed for 5-12 yr. No recurrence has been observed so far. These cases suggest that gastric plasmacytoma has a relatively good prognosis.