We identified 57 patients with relapsed or refractory AML treated with venetoclax and decitabine or azacitidine. The median age at diagnosis was 60 years (range, 23–81 years). Twenty-eight (49.1%) were male, and 76.8% identified as White. Patients were classified by ELN 2022 risk stratification: eight (14.0%) were favorable risk, 12 (21.1%) were intermediate risk, and 37 (64.9%) were adverse risk. The most common mutations were NPM1 (23.6%), NRAS (21.8%), and FLT3-ITD (20.0%). Twelve (22.6%) patients had diagnostic marrow samples consistent with AML with myelodysplasia-related changes (AML-MRC), and four (7.0%) patients had antecedent MDS.

We then assessed patient fitness at the time of diagnosis. The median CCI score was 4 (range, 2–14), and the median ECOG score was 1 (range, 0–3). We observed treatment strategies prior to salvage with venetoclax and a hypomethylating agent; 8 (14.0%) patients received an allogeneic stem cell transplant prior to venetoclax exposure, and 11 (19.3%) patients were previously exposed to a hypomethylating agent.

At the initiation of venetoclax-based salvage, 24 (42.1%) patients had relapsed disease, and the remainder (57.9%) had refractory disease to one or more lines of therapy. The overall cohort underwent a median of one prior line of therapy (range, 1–7). Patients received a median of two (range, 1–10) cycles of venetoclax and a hypomethylating agent. The baseline demographics of the study population are detailed in Table 1.

Fifty-three of 57 patients had toxicity data available for analysis; the frequencies of toxicities across all cycles are presented in Table 2. Two patients from the decitabine and azacitidine cohorts switched the hypomethylating backbone during maintenance, providing a total of 55 treatment courses evaluable for toxicity. The most common grade three or higher toxicities were hematologic. The most frequent grade three or higher hematologic toxicity was neutropenia, which occurred in 54 (98.2%) patients. There was a significantly lower rate of lymphocytopenia compared with the remaining hematological toxicities (p = 0.018), depicted in Fig. 2A. There were no significant differences in the rates of hematologic toxicities between the decitabine-venetoclax and azacitidine-venetoclax cohorts.

Toxicities associated with venetoclax and a hypomethylating agent in relapsed or refractory AML. A Frequencies of high-grade hematological toxicity; significantly fewer patients had grade 3 or higher lymphocytopenia compared with the remaining hematological toxicities (p = 0.018). B Causes of death in relapsed or refractory AML treated with venetoclax and a hypomethylating agent; death from underlying disease occurred significantly more frequently than any other cause (p < 0.0001)

We then analyzed the grade three or higher non-hematologic toxicities. Neutropenic fever was the most common (40.0%), followed by infection (38.2%) and hypotension (9.1%). Severe nausea, vomiting, and diarrhea each occurred at a rate of 3.6%. There were no significant differences in rates of non-hematologic toxicities between hypomethylating backbones.

Next, we analyzed the rates and causes of death. The rate of death within 30 days was 8.8%, and the rate of death within 60 days was 21.1%. There were no significant differences in the rates of death with respect to the hypomethylating backbone within 30 days (p = 0.639) or 60 days (p = 0.335). The cause of death was known in 40 (70.2%) of 57 patients. Thirty-one (77.5%) of 40 patients died from relapsed or refractory disease; in contrast, 15.0% died from organ failure, 12.5% from infection, and 5.0% from hemorrhage, as depicted in Fig. 2B. Death due to underlying disease was significantly higher than death from any other cause (p < 0.0001).

Fifty of 57 patients were evaluable for response. In the overall cohort, ten (20.0%) patients achieved CR, and ten (20.0%) achieved CRi. No patients achieved CRh. Nine (18.0%) patients had MLFS as the best response. The composite complete remission rate (CCR; CR + CRi) was 40.0% (95% CI, 27.6 to 53.8). The response data are presented in Table 3.

Next, we analyzed the responses with respect to the hypomethylating agent backbone. The CCR rate of decitabine-venetoclax was 33.3% (95% CI, 19.2 to 51.2), compared to 50.0% (95% CI, 29.9 to 70.1) for azacitidine-venetoclax; there were no significant differences in response between these cohorts (p = 0.258). We then analyzed responses after stratifying patients to the ELN 2022 risk categories. The CCR rate was 37.5% (95% CI, 13.7 to 69.4) for the favorable risk category, 36.4% (95% CI, 15.2 to 64.6) for intermediate risk, and 41.9% (95% CI, 26.4 to 59.2) for adverse risk. There were no significant differences in response between the ELN 2022 risk cohorts (p > 0.999). There were also no significant differences in response rates with respect to the hypomethylating agent backbone after stratifying by ELN 2022 risk categories.

We performed subgroup analyses to observe the responses after stratifying by prior treatment. There were no significant differences in response rates between relapsed disease and refractory disease (p = 0.572). While response rates numerically favored an azacitidine backbone for both relapsed and refractory disease, there were no significant differences in response rates between the hypomethylating agents. Additionally, there was no significant difference in response rates with respect to prior hypomethylating agent exposure before the initiation of venetoclax-based combination therapy (p = 0.450). The CCR rate was 33.3% in patients that underwent a stem cell transplant prior to venetoclax exposure and 40.9% in those that did not, which was not significantly different (p > 0.999).

We then analyzed responses in subgroups with specific disease phenotypes and molecular profiles. Patients with monocytic differentiation had a CCR rate of 22.2%, compared to 43.9% without monocytic differentiation (p = 0.285). The CCR rate was 50.0% in patients with prior MDS or AML-MRC, compared with 36.8% in de novo AML (p = 0.506). In patients that achieved a response to venetoclax and a hypomethylating agent and subsequently relapsed, the most common mutations at the time of relapse were in CBL, FLT3, or TP53—which represented 46.2% of new mutations after venetoclax failure. Patients who did not respond to venetoclax-based combination therapy showed significant enrichment in NRAS, KRAS, and FLT3-ITD, independent of mutated TP53 (p = 0.032). Conversely, patients who responded to venetoclax and a hypomethylating agent were significantly enriched in NPM1, IDH1, and IDH2 without co-mutations in NRAS, KRAS, or FLT3-ITD (p = 0.020).

Survival data were available for all 57 patients and are presented in Table 4. The median overall survival of the entire cohort was 8.2 months. Decitabine-venetoclax was associated with a non-significantly shorter overall survival at 5.7 months compared to azacitidine-venetoclax at 8.3 months (p = 0.425), as shown in Fig. 3A. The progression-free survival of the overall cohort was 4.6 months: when analyzed with respect to the hypomethylating agent, the progression-free survival of decitabine-venetoclax was 4.0 months compared to 5.6 months with azacitidine-venetoclax (p = 0.334).

Overall survival in cohorts of relapsed or refractory patients treated with venetoclax and a hypomethylating agent. A Overall survival of azacitidine-venetoclax was 8.2 months, compared to decitabine-venetoclax at 5.7 months (p = 0.425). B Overall survival of patients stratified by ELN 2022 risk category, with no significant differences between groups (p = 0.618). C Patients in MRD-positive CR had an overall survival of 20.4 months, compared to 4.3 months for MRD-positive MLFS (p = 0.035). D Patients with NPM1 or IDH mutations and no signaling mutations had an overall survival of 9.4 months, compared to 4.6 months for RAS or FLT3-ITD mutations (p = 0.026). E Patients with ECOG scores 0—1 had an overall survival of 8.2 months compared to 3.3 months for ECOG scores of 2—3 (p = 0.009). F A CCI score threshold of 5 or less is associated with superior survival at 9.2 months compared to scores of less than 5 at 4.4 months (p = 0.018)

Next, we investigated the impact of the procession to allogeneic stem cell transplant on survival. The median overall survival of patients that proceeded to transplant following treatment with venetoclax was non-significantly longer at 12.0 months, compared to 6.2 months for patients that forewent transplant (p = 0.125). Since all of the patients that proceeded to stem cell transplant did so in either CR or MLFS, we performed an ad hoc analysis to investigate the prognostic benefit of MRD-positive patients in CR or MLFS. We found that patients that achieved an MRD-positive CR had significantly superior overall survival at 20.4 months compared to MRD-positive MFLS at 4.3 months (p = 0.035, Fig. 3C). While a higher proportion of patients in MRD-positive CR proceeded to transplant, there was no significant difference in the receipt of transplant between the MRD-positive CR and MLFS cohorts (p = 0.200). We then compared patients who achieved MRD-positive MLFS and also did not undergo transplant to those that were refractory to venetoclax; there was no difference in overall survival between these cohorts (p = 0.480).

We subsequently analyzed the overall survival in patients stratified by the ELN 2022 risk categories. The median overall survival was 5.8 months for favorable risk, 8.2 months for intermediate risk, and 8.3 months for the adverse risk category, shown in Fig. 3B. There were no significant differences in the overall survival between any ELN 2022 risk cohorts (p = 0.618). Additionally, there was no difference in the overall survival when stratified by the ELN 2022 risk categories with respect to the hypomethylating agent backbone. To investigate this disparity, we analyzed the impact of IDH and RAS mutations in addition to existing mutations accounted for in ELN 2022 on overall survival. We discovered that IDH or NPM1 mutations are associated with a significant survival benefit at 9.4 months compared with at 4.6 months for mutated NRAS, KRAS, or FLT3-ITD (p = 0.026, Fig. 3D).

We then analyzed survival by patient fitness and comorbidities. Patients with an ECOG score of 0 to 1 had significantly superior overall survival at 8.2 months compared to 3.3 months for patients with an ECOG score of 2 to 3 (p = 0.009, Fig. 3E). To assess the impact of comorbidities on survival, we performed consecutive survival analyses starting with a Charlson comorbidity index (CCI) score of 3 and continued in increasing CCI score increments until a significant threshold was reached. We discovered that a CCI score threshold of 5 identifies patients at elevated risk of early death. Patients with a CCI score of greater than or equal to 5 had an overall survival of 4.4 months, and those with a score of less than 5 had a median survival of 9.2 months (p = 0.018, Fig. 3F).