PB2019 MOLECULAR ANALYSIS OF A COMPOSITE B‐CELL TUMOR – HAIRY CELL LEUKEMIA AND MANTLE CELL LYMPHOMA COMBINATION

Background: Composite lymphomas are unique models to study the clonal transformation process according stages of lymphoid cell differentiation. Clonal relationship is a key point in the research. At the moment, molecular analysis of V(D)J‐recombination is the most accurate method to evaluate related lymphoid populations. Aims: To study clonal rearrangements of IGH genes in isolated tumor populations in order to determine the mechanism of their occurrence during pathogenesis of composite lymphoma – hairy cell leukemia (HCL) and mantle cell lymphoma (MCL) combination Methods: Patient was diagnosed and treated at the National Research Center for Hematology. Informed consent was obtained. Isolation of MCL and HCL cells was carried out by magnetic selection of bone marrow leukocyte fraction using anti‐CD103 and anti‐CD5 magnetic particles according to the standard Miltenyi Biotec protocol ( www.miltenyibiotec.com ). B‐cell clonality testing and IGHV sequencing was performed according to BIOMED‐2 protocol. Fragment analysis and Sanger sequencing was performed on ABI PRISM 3100 genetic analyzer, followed by comparison with the germinal sequence databases www.imgt.org . Results: Patient was performed with leukopenia and lymphocytosis, splenomegaly, lymphadenopathy in May, 2018 and was diagnosed with HCL. The diagnosis was confirmed by the BRAF mutation detection and peripheral blood lymphocytes immunophenotyping (table 1). Patient was consistently treated with interferon α2b and cladribine with good partial response. Within 4 months after therapy was completed spleen repeatedly enlarged. Diagnostic splenectomy was performed and MCL was revealed. The diagnosis was confirmed by the t(11;14) detection. Immunophenotyping of spleen suspension allowed to identify not only MCL cells but minimal residual HCL population (table 1). Analysis of clonally rearranged IGH genes is isolated CD103+ and CD5+ population revealed two clonal products corresponding to components of composite lymphoma (figure 1). The sequence analysis identified the dissimilar repertoire of gene segments involved in V(D)J‐recombination in MCL (IGHV3‐9/IGHD2/IGHJ4) and HCL (IGHV1‐69/IGHD3/IGHJ4). This distinction indicated the independence of two clones’ origin, at least at the stage of B‐lymphocyte precursors as we do not have other molecular markers for progenitor lymphoid cells. Nucleotide sequence was 100% germinal in MCL and only 90% matches with the germinal sequence were detected in HCL reflecting the postgerminal phenotype. Thus not only the existence of separate tumor precursors was strictly supposed but also the different way of parallel lymphoid cell differentiation was proven. Patient was treated with R‐BAC cycles for MCL. Complete remission was achieved and has been maintained for 6 months. Summary/Conclusion: At the moment, there is no known description of the synchronous development of MCL and HCL. The presented clinical case is the first observation of the clinical course of such the composite lymphoma. We demonstrated independent origin of two tumor components and proved the different way of their differentiation. The proposed algorithm for the analysis of isolated cell populations and the obtained results make an additional contribution to the lymphomagenesis understanding, which is necessary for the development of effective methods of diagnosis and therapy.