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Spurious CD34 expression in B‐cell lymphoma due to nonspecific binding to PerCP‐Cy5.5 fluorochrome conjugates: A rare phenomenon and a diagnostic pitfall

Multi-color flow cytometry plays a critical role in distinguishing imma-ture from mature B-cell neoplasms by demonstrating CD34 and/or TdT expression on the neoplastic cells. We report the first case of a B-cell lymphoma nonspecifically binding PerCP-Cy5.5-conjugated CD34 antibody, mimicking B lymphoblastic leukemia/lymphoma (B-ALL/LBL). The patient is an 88-year-old male with a past medical history of bladder carcinoma, skin cancer, congestive heart failure, diabetes, and hyperlipidemia. He had an unintended 30 pounds weight loss for the past year without fever or night sweats. CBC showed Hb 6.8 g/dl, WBC 49 (cid:1) 10 9 /L, lymphocytes 41 (cid:1) 10 9 /L, and platelets 133 (cid:1) 10 9 / L. A CT scan demonstrated splenomegaly without lymphadenopathy. The peripheral blood smear revealed absolute lymphocytosis composed of mature-appearing small to medium-sized cells, with regular nuclear contours, variably condensed chromatin, inconspicuous nucleoli, and moderate amounts of cytoplasm Peripheral blood flow cytometry kappa light chain-restricted B-cell (88% of lymphocytes), for CD19, CD20, CD22, CD45, CD79a, CD5, CD10, CD103, and CD200 weakly bind to PerCP-Cy5.5, APC-Cy5.5, and Cy5.5 conjugates, but they do not bind to PE, PE-Cy5, Cy5, FITC, or Alexa488 conjugates (Park et al., 2012). These nonspecific interactions may pose an interpretation challenge and even cause a misdiagnosis.