Hairy Cell Leukemia: Hematological and Immunophenotypic Profile of 13 Patients

Introduction: Hairy cell leukemia (HCL) is a rare lymphoproliferative disorder of the mature B-cells, mostly seen in men, and is characterized by cytopenia, splenomegaly, myelofibrosis, and the presence of atypical lymphoid cells showing the cytoplasmic hairy projection in the peripheral blood, bone marrow, and spleen. The immunophenotypic (IPT) profile shows the clonal expansion of B-cells with CD19, CD20, and CD22 showing bright expression. The diagnosis requires two hairy cell markers out of CD103, CD123, CD25, and CD11c to be positive. The HCL variant (HCL-v) has a different IPT profile with negative CD25 in most cases.Aim: The aim was to study the hematological and IPT of classical HCL and HCL variants.Methods: This cross-sectional study included all the cases of HCL diagnosed over a retrospective period of eight years from 1st January 2015 to 31st December 2022 in a tertiary care hospital in north India. The patients included in the study were those for whom immunophenotyping; that is, flow cytometry and/or immunohistochemistry (IHC) were done for diagnosis. Bone marrow slides, IHC slides, and flow cytometric IPTs were reviewed.Results: The study included 13 patients who were diagnosed to have HCL, of which 12 were classical HCL and one was HCL-variant (HCL-v). Among classical HCL, IPT was done by flow cytometry in 10 patients, while in two patients, it was done by IHC. CD19, CD20, and CD22 were positive in all patients of classical HCL (10/10, 10/10, and 5/5, respectively), while CD123, CD103, CD25, and CD11C were positive in 100%, 89%, 80%, and 100% cases, respectively. One patient of HCL-v had CD103 and CD123 positive, while CD25 and CD123 were negative.Conclusion: The diagnosis of HCL requires a multipronged approach. The use of clinical features, morphology, and immunophenotyping combined with ancillary techniques provides higher diagnostic accuracy and enables its distinction from other B-cell lymphoproliferative disorders (BCLPDs), leading to better patient management and treatment.