Biphenotypic Acute Leukemia with t(15;17) Lacking Promyelocytic-retinoid Acid Receptor α Rearrangement.

Biphenotypic acute leukemias (BAL) account for less than 4% of all cases of acute leukemia. Philadelphia chromosome and 11q23 rearrangement are the most frequently found cytogenetic abnormalities. Since t(15;17) is almost always associated with acute promyelocytic leukemia, t(15;17) in BAL cases is extremely uncommon. We report here a rare and instructive case of BAL with t(15;17) and the successful treatment approach adopted. A 55-year old woman was referred to our hospital for an examination of elevated white blood cell (WBC) counts with blasts (WBC 13.4×109/L; 76% blasts). The blasts with acute lymphoblastic leukemia (ALL-L2, FAB) morphology coexpressed B-lymphoid and myeloid lineages, and a cytogenetic study revealed 4q21 abnormalities and t(15;17). However, promyelocytic-retinoid acid receptor α rearrangement was not detected by fluorescence in situ hybridization on interphase nuclei. Our patient was treated with chemotherapy for ALL and gemtuzumab ozogamicin without all- trans -retinoic acid, and has remained in hematologic first complete remission for more than 3.7 years.