Untangling the Strands of Hairy Cell Leukemia: The Clinicopathological Spectrum over Eleven Years at a Tertiary Care Center.

Background: Hairy Cell Leukemia (HCL) is an uncommon, indolent lymphoproliferative disorder of mature B lymphoid cells, accounting for 2% of all lymphoid tumors. The present study evaluated the clinical-hematological profile of HCL patients diagnosed at a single tertiary care center over a 11-year period.

Methods: The retrospective observational study was done between October 2010 and September 2021. The relevant clinical and laboratory information were retrieved from hospital medical records and electronic databases. The statistical analysis was performed using version 23.0 of SPSS.

Results: 66 (5.9%) of 1125 cases of chronic lymphoproliferative disorder were HCL. Splenomegaly was found in 47 (71.2%), hepatomegaly in 26 (39.5%), and lymphadenopathy in 17 (25.7%) of the cases. The mean hemoglobin, total leukocytes count, and platelets count were 8.04 g/dl, 6.76 X 109/L, and 77 X 109/L, respectively. Pancytopenia was detected in 40 cases (60.61 %). Bone marrow biopsies were majorly hypercellular and showed predominantly diffuse infiltration by atypical lymphoid cells. In two patients, initially thought of having refractory/hypoplastic anemia, the bone marrow biopsy and flow cytometry revealed HCL involvement.  42 cases of HCL underwent flow cytometry. CD20, CD 11c, CD 25 and CD 103 were positive in all the cases. The aberrant expression of CD5, CD10, and CD23 was found in frequencies of 5.71 %, 31.42 %, and 19.35%, respectively. In 40 cases for which follow-up information was available, there was full remission in 26 patients (65%), and later three showed relapse (7.5%) of which one died, and persistent leukemic activity in five (10%).  Eight patients (20%) died even before the initiation of treatment. One patient died within one month of therapy. No patient was examined for BRAF V600E mutation analysis.

Conclusion: CD 10+ HCL was the most prevalent atypical immunophenotypic subgroup. Bone marrow biopsy and flow cytometry are crucial diagnostic tools to rule out hairy cell leukemia. However, BRAF V600E mutation analysis should be performed in cases with unusual presentation or resistance to treatment.