Cytogenetic findings in patients with acute promyelocytic leukemia and a case of CML blast crisis with promyelocytic proliferation.

Nineteen patients with acute promyelocytic leukemia (APL) and one with promyelocytic blast crisis were studied by a methotrexate cell synchronization technique and by 24-hour short-term culture. Nineteen cases of APL included two cases of the microgranular variant (M3V). Except in one case of M3V, t(15;17) was detected in all patients. The breakpoints were determined as 15q22 and 17q12-21. A chronic myeloid leukemia (CML) blast crisis patient with high promyelocyte count also had a t(15;17) as well as a masked Ph chromosome. Other abnormalities, such as +8,del(7q) and an i(17q), were also observed in some patients. Our studies have indicated that 1) the translocation (15;17), characteristic of APL, was present in our population in almost all patients; 2) the presence of an identical abnormality in a promyelocytic CML blast crisis supported and confirmed the phenomenon of association of specific chromosome change with target cell type; and 3) the precise localization of breakpoints on chromosome 17 is still difficult to determine. The identification of as yet unknown genes at region 17q11-q21 and their subsequent translocation on chromosome 15 will help in assigning a precise position to these breakpoints.