Near-triploid Ph-positive leukemia.

Tetraploid populations have been observed in various types of leukemia, but relatively few reports exist of triploid cell populations in acute or chronic leukemia. We report two cases of Ph-positive leukemia with a modal triploid cell population. Examination of peripheral blood from a 3-year-old boy with Ph-positive acute lymphoblastic leukemia (ALL) and a 68-year-old male with Ph-positive chronic myelocytic leukemia (CML) in blastic crisis revealed modal populations of 72 and 63 chromosomes, respectively. G-banding analysis of both cases revealed the following: karyotypic instability (no clonality), dominant trisomy, and the random association of the Ph chromosome with gains and losses of chromosomes involved in this translocation. The cytogenetic evidence obtained suggests that the triploid cell populations were not derived from a duplication of a hypodiploid cell population, but resulted from random loss of chromosomes from tetraploid cell populations derived from duplication of pseudodiploid cells.