Abstract
Simple SummaryHairy cell leukemia (HCL) is a rare B cell neoplasm that accounts for 2% of B-cell lymphomas. The diagnosis was based on the presence of abnormal lymphoid cells that expressed CD103, CD123, CD25 and CD11c. The aim of this retrospective study was to describe the immunophenotypic profile of HCL and HCL-like disorders using 13 markers and to assess the added value of immunophenotypic row data and unsupervised analysis. We confirmed that the immunological profile alone is not sufficient and that morphologic, phenotypic and molecular data need to be integrated.Hairy cell leukemia (HCL) is characterized by abnormal villous lymphoid cells that express CD103, CD123, CD25 and CD11c. HCL-like disorders, including hairy cell leukemia variant (vHCL) and splenic diffuse red pulp lymphoma (SDRPL), have similar morphologic criteria and a distinct phenotypic and genetic profile. We investigated the immunophenotypic features of a large cohort of 82 patients: 68 classical HCL, 5 vHCL/SDRPL and 9 HCL-like NOS. The HCL immunophenotype was heterogeneous: positive CD5 expression in 7/68 (10%), CD10 in 12/68 (18%), CD38 in 24/67 (36%), CD23 in 22/68 (32%) and CD43 in 19/65 (31%) patients. CD26 was expressed in 35/36 (97%) of HCL patients, none of vHCL/SDRPL and one of seven HCL-like NOS (14%). When adding CD26 to the immunologic HCL scoring system (one point for CD103, CD123, CD25, CD11c and CD26), the specificity was improved, increasing from 78.6% to 100%. We used unsupervised analysis of flow cytometry raw data (median fluorescence, percentage of expression) and the mutational profile of BRAF, MAP2K1 and KLF2. The analysis showed good separation between HCL and vHCL/SDRPL. The HCL score is not sufficient, and the use of unsupervised analysis could be promising to achieve a distinction between HCL and HCL-like disorders. However, these preliminary results have to be confirmed in a further study with a higher number of patients.
Highlights
Hairy cell leukemia (HCL) and HCL-like disorders, including hairy cell leukemia variant, splenic diffuse red pulp lymphoma (SDRPL) and splenic marginal zone lymphoma (SMZL) with villous lymphoid cells, are characterized by a similar morphologic examination, with the identification of hairy cells in the blood and bone marrow and a distinct phenotypic and genetic profile, a different clinical course and the need for appropriate treatment.Initially described in 1958 [1], HCL is a well-defined and distinct entity in the 4th revised 2017 classification of the World Health Organization (WHO) of hematopoietic and lymphoid tumors [2]
We investigated a large series of 82 patients with HCL or HCL-like disorders in a single center by flow cytometric immunophenotyping (FCI)
CD11c was bright in all cases, and the MFI was higher in HCL than in HCL-like
Summary
Hairy cell leukemia (HCL) and HCL-like disorders, including hairy cell leukemia variant (vHCL), splenic diffuse red pulp lymphoma (SDRPL) and splenic marginal zone lymphoma (SMZL) with villous lymphoid cells, are characterized by a similar morphologic examination, with the identification of hairy cells in the blood and bone marrow and a distinct phenotypic and genetic profile, a different clinical course and the need for appropriate treatment.Initially described in 1958 [1], HCL is a well-defined and distinct entity in the 4th revised 2017 classification of the World Health Organization (WHO) of hematopoietic and lymphoid tumors [2]. Hairy cell leukemia (HCL) and HCL-like disorders, including hairy cell leukemia variant (vHCL), splenic diffuse red pulp lymphoma (SDRPL) and splenic marginal zone lymphoma (SMZL) with villous lymphoid cells, are characterized by a similar morphologic examination, with the identification of hairy cells in the blood and bone marrow and a distinct phenotypic and genetic profile, a different clinical course and the need for appropriate treatment. The median age of patients at diagnosis is 63 years in men and 59 years in women [4]. The diagnosis is based on the identification of characteristic hairy cells involving peripheral blood and diffusely infiltrating the bone marrow and the splenic red pulp. The BRAF-V600E mutation in the B-raf proto-oncogene (BRAF gene) (7q34), which is detected in 80–90% of HCL cases, is identified in various solid tumors such as melanoma [5]. The mutation mimics phosphorylation independently from RAS, resulting in constitutive kinase activity
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