The pathologic features of acute promyelocytic leukemia (APL) with t(15;17)(q22;q21) are highly characteristic, which with few exceptions enable a firm diagnosis to be made on morphologic grounds. An APL patient in first relapse presented with large, bizarre circulating blasts and bone marrow necrosis 2 weeks after chemotherapy consolidation for an arsenic trioxide-induced remission. Although a morphologic diagnosis could not be reached, cytogenetic investigations showed a near-triploid clone with t(15;17), confirming APL in second relapse. This case showed that clonal evolution with additional karyotypic aberrations might alter the blast morphology and pathologic features in APL.
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