PB1028 - Complete non-cytotoxic drug induction therapy in Acute Promyelocytic Leukemia：a single-center prospective single-arm clinical observational Study

Background: During the induction therapy of acute promyelocytic leukemia (APL), the combination of all-trans retinoic acid (ATRA) and arsenic trioxide (ATO) has achieved widespread utilization. However, this treatment often results in leukocytosis in patients. According to clinical guidelines, the use of cytotoxic agents is recommended for the purpose of decreasing the white blood cell (WBC), but it is associated with severe bone marrow suppression, fatal infections.

Aims: By monitoring changes in blood routine and coagulation parameters during ATRA+ATO induction responses, we aim to observe the association between WBC counts and induction differentiation syndrome (DS), and so on.

Methods: This study is a single-center, prospective, single-arm observational study. We recruited 26 newly diagnosed APL patients (WBC≤20000/mcl), including 3 high-risk and 23 low-risk patients. We used the ATRA+ATO for induction therapy and monitored patients' treatment responses through blood routine tests and coagulation index .For patients with increased WBC counts during induction treatment, we attempted to avoid using any cytotoxic drugs, including anthracyclines and hydroxyurea. Dexamethasone was administered intravenously for suspected early signs of DS.

Results: This study included 26 APL patients, and all patients achieved CR. Among them, 18 patients had a peak WBC count exceeding 20000/mcl, with the highest peak WBC count (WBC count of 124000/mcl) being 114 times higher relative to the pre-treatment count compared to pre-treatment levels. The median time to reach the peak WBC count was 15.5 days (10-25). Importantly, despite the increase in WBC, the proportion of promyelocytes gradually decreased, and no severe DS was observed, eliminating the need for cytotoxic drugs to reduce WBC.

Conclusion(s): With monitoring, it is possible to completely avoid the use of cytotoxic drugs to reduce WBC and minimize unnecessary risks of infection during the induction therapy of APL using ATRA+ATO. The increase in WBC count (WBC≥10000/mcl) is not the factor for the administration of cytotoxic drugs.