PB2063 HAIRY CELL VARIANT–LABORATORY FINDINGS OF A CASE SERIES

Background: Hairy cell leukemias are rare mature B‐cell neoplasms that morphologically present cytoplasmatic projections. According to the most recent World Health Organization Classification, they can be Classic (HCL) or Variant (HCLv). These two diseases present important clinical and laboratory differences. HCLv is the rarest of them with an incidence of less than 1 case:1.000.000 inhabitants/year. Unlike HCL, HCLv generally presents with elevated blood counts, there is no monocytopenia and the abnormal cells present an identifiable nucleolus. HCLv cells do not express CD25 or present BRAF mutation mutations, findings that are almost universally present in HCL. Aims: The aim of this study was to describe the laboratory findings of all HCLv cases diagnosed at Grupo Fleury from 2015 to 2018. Methods A retrospective descriptive study of the laboratory findings of all HCLv cases diagnosed at Grupo Fleury from 2015 to 2018. Complete blood counts were obtained with a Sysmex XE 5000 counter and submitted to morphology review. Blood or bone marrow immunophenotypic prophiles were obtained using an 8‐color FACS Canto II cytometer for acquisition and Inifinicyt for analysis. Antibodies against CD3, CD4, CD5, CD8, CD10, CD11c, CD19, CD20, CD22, CD23, CD25, CD38, CD45, CD56, CD79b, CD103, CD123, CD200, KAPPA, LAMBDA, FMC7, IgM, IgD, IgG and IgA were used. Results: 7 cases were diagnosed during this period (0.04% of all of suspected oncological cases submitted immunophenotyping). Median age was 86 years old (range: 58‐89), and 3 were males. Median CBC values were [median (range)]: hemoglobin = 10.1 g/dL (8.8‐12.7); lymphocytes = 2.4 × 10 9 /L (1.4‐16.5); monocytes = 0.53 × 10 9 /L (0.2‐3.1); platelets = 91 × 10 9 /L (76‐97, and an outlier of 1.106 × 10 9 /L). No cases presented monocytopenia Flow cytometry (5 of peripheral blood and 2 of bone marrow aspirate), demonstrated universal positivity for CD19, CD20, FMC‐7, CD103, and CD11c (partial expression in one case). No case demonstrated CD5, CD10, CD25, CD38 or CD123. Of note, CD200 expression was negative or mild in all cases. Five cases were IgM+/IgD+, one IgM+, and the other was IgG+. Two demonstrated kappa expression and 5 were lambda light chain restricted. Karyotype was normal in all of the 3 cases analyzed. Summary/Conclusion: Flow cytometry, along with morphology, was the main sources of diagnosis, as no specific genetic alteration is known. The presence of CD103 and CD11c in the absence of CD123 and CD25 suggest HCLv, excluding classical HCL. CD200, classically strongly expressed in classical HCL was negative or only weakly expressed in HCLv and may help on diagnosis.