Background: Venetoclax (Ven) has synergistic activity with hypomethylating agents (eg, azacitidine [Aza] or decitabine [Dec]) or low-dose cytarabine (LDAC). These Ven-based combinations have demonstrated rapid median response times. This analysis describes the rapidity and likelihood of response to Ven treatments, and its associated characteristics, in older patients with newly diagnosed acute myeloid leukemia (AML). Methods: Included are data from two open-label trials of Ven, at label recommended doses, in combination with Aza, Dec (NCT02203773; phase 1b), or low-dose cytarabine (NCT02287233; phase 1/2) in newly diagnosed patients with AML. Patients were classified based on CR/CRi timing: within 2 cycles of therapy, after 2 cycles, or never achieving CR/CRi. Within each group, baseline and post-baseline characteristics were evaluated to determine impact on response timing. The percentage of patients in each category and duration of response (DOR) in each category were also evaluated. Results: Data cutoff was August 2018. Of 197 patients, 42% (n = 83) had CR/CRi in ≤2 cycles, 22% (n = 44) had CR/CRi in > 2 cycles, and 36% (n = 70) did not achieve CR/CRi. Median DOR was 21.2 mos. (95% CI 14.1-NR) for ≤2 cycle responders and 8.1 mos. (95% CI 5.3-14.9) for > 2 cycle responders. Baseline characteristics are shown in the Table. Patients with baseline IDH1/2 mutation were more likely to have CR/CRi in ≤2 cycles, while those with secondary AML and no response by the end of cycle 2 were more likely to never achieve CR/CRi. Of the patients who achieved CR/CRi after 2 cycles of therapy, 43% (19/44) achieved MLFS within the first two cycles. Of those who never achieved CR/CRi, 17% (12/70) of patients achieved MLFS within 2 cycles. In depth regression analyses of factors predictive of response, including analysis of biomarkers, will be available upon presentation. Conclusions: Over 1/3^rd of patients that achieved CR/CRi on Ven combination therapy within these two studies required more than 2 cycles of treatment. Therefore, prior to discontinuing therapy for nonresponders, it is critical to assess key predictive patient characteristics. Clinical trial information: NCT02203773 and NCT02287233.

* No mitosis detected in n = 1, 1, and 6 patients respectively