Sister chromatid exchange in Philadelphia chromosome (Ph1)-positive leukemia.

The sister chromatid exchange (SCE) frequency was studied in the leukemic cells of 12 patients, 10 with Philadelphia chromosome (Ph1)-positive chronic myelocytic leukemia (CML), 1 with Ph1-negative CML, and 1 with acute myeloblastic leukemia. Except for two patients in the blastic phase of CML, the SCE values were within the normal range [3.8 +/- 6.4 (S.D.) SCE/cell; normal is 3.3 +/- 2.2 SCE/cell]. In the two cases with the blastic phase of CML, the values were 7.6 +/- 3.2 and 8.9 +/- 4.7 SCE/cell, a statistically significant difference from the control values. However, in the patient with acute myeoblastic leukemia, the SCE incidence increased from 3.6 to 24.4 SCE per cell when therapy was changed to daunorubicin and vincristine and the disease became progressive. Further studies on SCE and leukemia may prove the usefulness of this determination for therapeutic and clinical purposes.