Recognizing non-neoplastic mimics of lymphoid malignancies in the bone marrow and peripheral blood: pearls and pitfalls

Non-neoplastic mimics of lymphoid malignancies are common in the bone marrow and peripheral blood. They include benign reactive lymphoid populations and pre-malignant conditions. The distinction between benign, pre-malignant, and lymphoma is vital for patient care. In this article, we present our approach to peripheral blood lymphocytosis, lymphocytes with abnormal morphology or unexpected immunophenotype, circulating clonal lymphocytes, and bone marrow lymphoid infiltrates. We focus on practical pearls and pitfalls, with an emphasis on key mimics to exclude before making a lymphoma diagnosis. Summary tables are included for reference and figures include histology, immunohistochemistry and flow cytometry examples.