Persistent polyclonal B-cell lymphocytosis with buttock-like cells mimicking follicular lymphoma.

A 52-year-old woman was found to have leukocytosis [19.4×10 9 /L (range, 4 – 11)] with absolute lymphocytosis [5.8×10 9 /L (range, 1 – 4.8)] for ∼ 1 year. Peripheral blood (PB) showed circulating atypical, binucleated and clefted lymphocytes mimicking “buttock cells” of follicular lymphoma. PB flow cytometry (FC) showed polytypic B-cell lymphocytosis (64.4%) expressing CD19 + CD20 + CD27 + IgM + and CD5 - CD10 - CD38 - . No cutaneous lesions were noted. A staging bone marrow showed no evidence of lymphoma. Cytogenetics showed a normal female karyotype. Serum IgM levels were increased [8.4 g/L (range, 0.35 – 2.4)], with normal IgA and IgG levels. Serum protein electrophoresis and immunofixation studies showed no M-protein. PET-CT showed no lymphadenopathy or hepatosplenomegaly. She had 30-years smoking history. Based on the above findings, persistent polyclonal B ‐ cell lymphocytosis (PPBL) was diagnosed. PPBL is a benign proliferation of memory B-cells in adult women with longstanding smoking history. Exact pathogenesis of PPBL is not known, potential mechanisms include defect in CD40 activation pathway or expansion of functional CD27 + memory B-cells. About 90% of PPBL cases are HLA-DR7-positive