Dynamic changes and multiplication rate of white blood cell count may direct the timing of cytoreduction chemotherapy during induction treatment in newly diagnosed acute promyelocytic leukemia with low-intermediate risk.

In order to explore the optimal timing for initiating cytoreduction chemotherapy following all-trans retinoic acid plus arsenic trioxide administration, 58 newly diagnosed patients with acute promyelocytic leukemia (APL) with low-intermediate mortality risk were retrospectively analyzed. During induction treatment, white blood cell (WBC) count >4x10/l and multiplication rate of WBC <3 days were defined as rapid WBC multiplication. Patients were divided into two groups: With or without rapid WBC multiplication. Comparison between the two groups revealed that the incidence of differentiation syndrome (DS) (48.1% vs. 6.5%; P<0.001), grade 3-4 bleeding (34.8% vs. 6.5%; P=0.022) and peak WBC count (30.4±20.0x10/l vs. 8.67±5.4x10/l; P<0.001) were significantly higher in the group with rapid WBC multiplication compared with in the group without rapid WBC multiplication. No significant differences were observed in bone marrow depression, infection, complete remission (CR) rate, time to achieve CR and early mortality rate between the two groups. Multivariate analysis revealed that WBC count at chemotherapy initiation was an independent risk factor for the occurrence of DS (P=0.040). Peak WBC count and rapid WBC multiplication were significantly associated with grade 3-4 bleeding (P=0.019 and P=0.002, respectively). Hence, WBC count at chemotherapy initiation along with its multiplication rate may direct the timing of cytoreduction chemotherapy during induction treatment in newly diagnosed APL with low-intermediate risk.