Lymphoid aggregates in bone marrow mimic residual lymphoma after rituximab therapy for non-Hodgkin lymphoma.

Abstract

Rituximab is a novel anti-CD20 monoclonal antibody used in the treatment of relapsed low-grade non-Hodgkin lymphoma. To determine the impact of this therapy on the interpretation of posttherapy specimens, we reviewed the pretherapy and posttherapy bone marrow and peripheral blood morphologic and flow cytometric findings for 20 patients who received rituximab. Nine patients had a total of 13 posttherapy bone marrow specimens; all were positive for lymphoma before therapy. After therapy, 11 of 13 posttherapy bone marrow specimens were interpreted as positive or suggestive of lymphoma based on routine H&E-stained sections. However, immunohistochemical and/or flow cytometric immunophenotyping showed that 6 of the 11 cases were negative for lymphoma; the lymphoid infiltrates were composed entirely of T cells without B cells. We report that posttherapy bone marrow specimens from patients treated with rituximab may mimic residual lymphoma if examined by morphologic features alone. Familiarity with this finding and the use of ancillary immunophenotypic studies will aid in the accurate interpretation of posttherapy specimens.