Transformation of bilineal hybrid acute leukemia to acute lymphoid leukemia: A case report with serial analyses of cytogenetics and gene rearrangement

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Abstract
A 17‐year‐old male with bilineal hybrid acute leukemia is described. Two‐color flow cytometric analysis of blast surface phenotype revealed that there were two groups of blasts which showed either CD 10+ CD 19+ CD 13− CD 33− or CD 10− CD 19− CD 13+ CD 33+, but not both. He developed a complete remission by treatment with vincristine, prednisolone, adriamycin, and L‐asparaginase. After 8 months, however, leukemia relapsed and lymphoid blasts were dominant. Cytogenetic analysis at presentation showed 46, XY, t(3;9)(p21;p22), and at relapse it showed 46, XY, t(1;3;9)(1 pter→1 q32::3p25→3pter; 3qter→3p21::9p22→9pter;9qter→9p22::3p21→3p25::1q32→1qter), t(2;19)(p21;q13). Analysis of the heavy chain joining region at diagnosis showed three hybridizing bands, all rearranged, but at relapse only one rearranged band. Analysis of the constant region for the β T‐cell receptor gene (TCRβ) both at diagnosis and at relapse showed one rearranged and one germline band, suggesting that rearrangement of one allele of TCRβ of not only lymphoid but also myeloid blasts occurred. It is considered that the target cell of lymphoid leukemia cells and that of myeloid leukemia cells at diagnosis were the same, which differentiated to two lineages, and the clone which evolved from lymphoid lineage proliferated at relapse.