Disappearance of CD 20 after treatment with rituximab of mantle cell lymphoma

: A 60-year-old female visited our hospital in May 2001 because of systemic lymphadenopathy. Her white blood cell count was 25,510/microliters with 93% of lymphocytes. Bone marrow aspiration revealed that 86% of nucleated cells were lymphocytes. Lymphocytes in the peripheral blood and bone marrow were positive for CD 5, 19, 20, and sIgx and negative for CD 23. FISH analysis detected the chimeric bcl 1/IgH fusion gene. Immunohistochemistry of a biopsied lymph node revealed that lymphoma cells were positive for cyclin D 1. Mantle cell lymphoma (MCL) was diagnosed at clinical stage IV A. Although a partial remission was obtained after CHOP plus rituximab therapy, the patient's disease recurred in March 2002 and she died in spite of salvage therapy including rituximab. Immunohistochemistry of the bone marrow cells after salvage rituximab therapy revealed that lymphoma cells were still positive for CD 5 and cyclin D 1, but negative for CD 20 and sIgx. We could not exactly determine how frequently CD 20 expression becomes negative in B-cell lymphomas after treatment with rituximab. We found only two reported cases that suggested rituximab down-regulated CD 20 expression in MCL. We herein describe a case of MCL with very notable clinical features.