B-lymphoblastic transformation of mantle cell lymphoma/leukemia with 'double hit' changes.

Mantle cell lymphoma is a mature B-cell neoplasm composed of small to medium-sized atypical lymphocytes and has a characteristic t(11;14)(q13;q32) translocation, with a variably aggressive and overall incurable course. More aggressive histologic variants have been described, as well as rare cases of transformation to other large cell lymphomas. Here, we describe a novel case of large cell blastic transformation of mantle cell lymphoma/leukemia at presentation with unusual immunophenotypic and cytogenetic features, most consistent with B-lymphoblastic leukemia. Morphologic findings include sheets of large blasts replacing the bone marrow, as well as occasional small to medium-sized atypical lymphocytes in the background. The blasts express CD19, PAX5, CD10, Cyclin D1, and TdT but are negative for CD5, CD20, and BCL2 by immunophenotyping. Cytogenetic studies show a complex karyotype with t(11;14), monosomy 13, gains of 8q, and MYC gene rearrangement and amplification among other changes. This unique case of blastic TdT-positive B-cell leukemia arising from mantle cell lymphoma may represent transformation with complex cytogenetic abnormalities including 'double hit' changes. This distinctive presentation may expand our understanding of the biology behind mantle cell lymphoma progression. [ABSTRACT FROM AUTHOR]