The utility of CD20 immunohistochemistry in the evaluation of staging bone marrow biopsies of newly diagnosed diffuse large B-cell lymphomas (DLBCL) patients has not been extensively studied. We used 113 routinely processed bone marrow biopsies to study the extent and pattern of involvement by lymphoma and CD20 staining. Twelve (10.6%) of 113 cases had involvement by morphology, and five (41.7%) of these showed histologic discordance between the primary site and the bone marrow. All cases with morphologic evidence of bone marrow involvement showed staining for CD20. Four (3.5%) of 113 cases had non-neoplastic aggregates that stained for CD20. One case (0.9%) showed a small benign lymphoid aggregate by immunohistochemistry that was not evident by morphology. Our results demonstrate that CD20 staining did not detect any examples of bone marrow involvement by DLBCL that were not evident by morphology. We conclude that immunohistochemistry for CD20 adds no increase in the sensitivity of detection of bone marrow infiltration by DLBCL.
Keywords: Diffuse large B-cell lymphoma, bone marrow, staging, immunohistochemistry, CD20