White Blood Cell (WBC) Count

The prognostic significance of WBC count is used to define high-risk and low-risk patient populations and to assign induction treatment. High-risk patients are defined by a WBC count of 10 × 109/L or greater.[1,2] Patients with high-risk acute promyelocytic leukemia (APL) are given an anthracycline (idarubicin) along with induction therapy. Postinduction therapy is the same for both standard- and high-risk APL.[3]

APL in children is generally similar to APL in adults, although children have a higher incidence of hyperleukocytosis (defined as a WBC count higher than 10 × 109/L) and a higher incidence of the microgranular morphological subtype.[4-7] As in adults, children with WBC counts of less than 10 × 109/L at diagnosis have historically had better outcomes than patients with higher WBC counts.[5,6,8] Presenting WBC count is still used to determine induction therapy. However, with modern tretinoin- and arsenic trioxide–based therapy, patients with high-risk APL have similar excellent survival rates as patients with standard-risk APL.

In the Children's Oncology Group (COG) AAML0631 (NCT00866918) trial, which included treatment with chemotherapy, tretinoin, and arsenic trioxide, patients were stratified on the basis of WBC count to standard risk or high risk. Risk classification primarily defined early death risk rather than relapse risk (standard risk, 0 of 66 patients vs. high risk, 4 of 35 patients).[9] In the COG AAML1331 (NCT02339740) trial, patients were treated with tretinoin and arsenic trioxide along with aggressive supportive care measures. There was only 1 death (standard-risk APL) and 3 relapses (1 standard risk and 2 high risk) reported among 154 patients. Thus, no significant differences were seen between the risk groups.[3] In the COG AAML0631 (NCT00866918) and AAML1331 (NCT02339740) trials, relapse risk after remission induction was 4% and 2% overall, respectively.[3,9]