Tetraploidy and Y chromosome loss in acute mixed-lineage leukemia

An unusual case of acute leukemia with mixed phenotype was followed up from diagnosis to death for about 12 months. The first cytogenetic examination revealed about 80% of the bone marrow cells in the diploid and 20% in the tetraploid range. After two courses of induction therapy, complete remission was achieved within 2 months. At this time the tetraploid cells were reduced to 3%, but 50% of the mitoses showed a Y chromosome loss, while the other mitoses had a diploid karyotype. Early intensification therapy was given 6 weeks later with slow recovery of blood counts. After four months a sharp decrease of the number of Y-missing mitoses was observed, while the marrow remained in full remission. Two months later a relapse occurred and the patient died. At this time the -Y clone had dropped to 2% and the tetraploid clone was totally absent. We conclude from these findings that the diploid clone was the most malignant one, whereas the -Y cells were probably not directly involved in the leukemic process.