Introduction:Hairy Cell Leukemia (HCL) is a B-cell non-Hodgkin's Lymphoma (B-NHL) representing about 2% of chronic leukemias, is manifested in adults with an average age of 55 years old or more and the ratio of male: female is 5:1, being more common among white people. It is characterized by the presence of neoplastic lymphocytes with cytoplasmic projections (villous cells), a characteristic commonly observed in other DLPCs such as variant HCL (HCL-v) and splenic villous cell lymphoma (SVCL), being the immunophenotyping by flow cytometry determinant in the differential diagnosis of these neoplasms. HCL is characterized by splenomegaly, hepatomegaly, pancytopenia in peripheral blood (PB) with leukopenia, anemia, neutropenia, monocytopenia, and thrombocytopenia. It has a low number of circulating tumor cells, spleen, liver, and bone marrow (BM) infiltration.Objective:To investigate, by flow cytometry, patients with lymphocytosis and presence of villous lymphocytes in the characterization of HCL and HCV-v and SMZL.Methodology:Were investigated samples of peripheral blood (SP) and bone marrow (MO) from 27 patients previously diagnosed with DLPC and presence of villous lymphocytes which were by flow cytometry with a panel of monoclonal antibodies (MoAb) conjugated to fluorochromes and targeted to T-lymphocytes: CD1a, CD2, CD3, CD5, CD7, subpopulation T-helper (CD3/CD4) and T-cytotoxic (CD3/CD8), in addition to TCR a/b and TCR g/d; Natural Killer cells: CD16-56; B-lymphocytes: CD19, CD20, CD21, CD22, CD23, CD79b, CD200, IgM, IgG, IgD, anti-kappa and anti-lambda, in addition to CD10, TdT (Terminal deoxynucleotidyl Transferase), CD103, CD123, CD11c, CD25, CD38, CD138, CD45 and CD14. At the same time, a complete blood count with differential white blood cell count and investigation of clinical and demographic data such as age, sex and ethnicity / race were also performed.Results:The distribution of patients according to ethnicity and gender, there was a predominance of white individuals and males. The age group most affected was in patients older than 60 years. All patients expressed pan-B antigens on leukemic cells with expression of CD19, CD22 / CD20 (Forte), sIgH, associated with clonal restriction for immunoglobulin light chain (kappa= 20 and lambda= 7), associated with FMC7 expression, HLADR, CD38 and CD45 strong and negativity to CD10, CD138, CD200, CD23, CD5, TdT and related T antigens. Sixteen cases were categorized as HCL, six HCLv and five SVCL. The immunophenotyping of HCL cases was positive for CD103, CD25, CD123 and CD11c. HCLv was negative for CD103 in three cases and CD25 and SVCL negative for CD103, CD123 and CD11c and CD25 in all cases.Conclusions:The precise diagnosis of HCL has fundamental importance because each NHL-B has a specific treatment, besides emphasizing the sensitivity and speed of the IFC regarding diagnosis and follow-up.

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