DNA-RNA measurements in patients with acute leukemia undergoing remission induction therapy

Prior to therapy, 111 newly diagnosed adult patients with acute leukemia had DNA content measured (cell-cycle distributions) and 91 had RNA content measured using flow cytometry of acridine orange-stained bone marrow biopsies. The RNA index (RI) (ratio of mean RNA in G₀/G₁ of the sample to the median RNA in G₀/G₁ of normal lymphocytes) distinguished acute myelogenous leukemia (AML) from acute lymphocytic leukemia (ALL). The mean RI in AML was 2.2 and in ALL 1.5. RI did not predict for achievement of complete remission (CR). In AML the mean S-phase percent was 11.2 in patients who achieved CR and 13.1 in those who failed to respond to therapy, whereas in ALL it was 14.5 in those responding and 8.0 in those not responding (P = .02). In the 77 patients with either AML or ALL who achieved CR, a low pretreatment S-phase percent and a high RI correlated with a long duration of CR. S-phase percent and RI were also measured during remission induction and during maintenance therapy. Between days 8 and 18, the RI of responders decreased. In both AML and ALL an increase in S-phase percent between days 18 and 22, prior to morphological CR, was observed in responders but not in nonresponders. The mean S-phase percent at the time of morphological remission was 17.3. A high S-phase percent at this time correlated with a longer duration of CR. Although neither pretreatment S-phase percent nor RI was found to predict for achievement of CR in AML, both predicted for length of CR. Increases in S-phase percent during therapy indicated recovery of normal hematopoiesis.