Biphasic acute myeloid leukemia with near-tetraploidy and immunophenotypic transformation.

This report describes a case of acute myeloid leukemia (subtype M1) with biphasic morphology. The bone marrow biopsy showed 2 distinct regions of blasts, one containing large cells and the other small cells. Morphometric and DNA ploidy analysis showed that the mean nuclear area and mean DNA index for the large cell region were 2-fold higher than those for the small cell region. Cytogenetic analysis showed an abnormal near-tetraploid clone. The tumor relapsed following aggressive therapy. The cells from the relapse specimen were similar to the original small cell region with respect to nuclear area and DNA index; however, there was immunophenotypic transformation with gain of CD7 and gain of CD56. Cytogenetically, the relapse specimen showed no evidence of the near-tetraploid clone, but instead had a previously unidentified abnormal clone containing 46 chromosomes and structural abnormalities of 2q and 7q. Biphasic morphology in acute myeloid leukemia may be predictive of a near-tetraploid subclone and immunophenotypic transformation.