Acute Myeloid Leukemia (AML) Treated with Azacitidine: Survival Outcomes for Patients Who Complete More Than Six Cycles Are Similar to High-Risk Myelodysplastic Syndrome/Low Blast Count AML

INTRODUCTION: Despite accumulating evidence supporting the efficacy of hypomethylating agents in patients with AML and > 30% bone marrow blasts as well as in relapsed/refractory AML, this therapy is not yet funded by National Health Plans / Healthcare Funding Agencies in a number of countries including Canada. The assistance of an industry-sponsored compassionate program has enabled provision of azacitidine for this group of patients at The Ottawa Hospital. We report here our local "real-world" experience of azacitidine efficacy in this diverse group of AML patients and identify a sub-group whose outcomes are equivalent to that of patients with higher-risk Myelodysplastic Syndrome (MDS) and AML with 20-30% blasts for whom azacitidine therapy has funding approval in Canada.

METHODS: All patients who received azacitidine at The Ottawa Hospital between 2009 and 2016 were included in this single-center, retrospective analysis. Azacitidine was administered at a dose of 75mg/m² subcutaneously daily for 7 consecutive days every 28 days. Response was evaluated with a repeat bone marrow aspirate and trephine biopsy after the 6^th cycle. In those patients confirmed to have stable or responsive disease, azacitidine was continued until progression of disease, intolerable side-effects of the drug or the patient chose to discontinue therapy. Overall survival curves were generated using the Kaplan-Meier method and log-rank tests were used to compare subgroups of patients. Actuarial median survival months were calculated with 95% confidence intervals (CI). P-values less than 0.05 were considered statistically significant.

RESULTS: During the study period, 109 patients received azacitidine: 54 had MDS /AML with 20-30% blasts (the 'funded' group) and 55 had either AML with > 30 % blasts (n=23), AML relapsed post-intensive chemotherapy (n=14), AML relapsed post-allogeneic stem cell transplant (n=10) or primary refractory AML (n=8) (the 'unfunded' group). Median survival of the 'funded' group was 12.2 months while median survival of the 'unfunded' group was 5.6 months (95% CI 3.3-7.7; p=0.0058). Of the AML patients in the 'unfunded' group, 24% completed more than 6 cycles of azacitidine compared to 52% of patients in the 'funded' group. In both the 'funded' and 'unfunded' groups, patients who completed more than 6 cycles of azacitidine had similar survival outcomes (p=0.7277): the 'funded' group had a median survival of 19 months (95% CI 14.4-25.3) while the median survival of this sub-population of the 'unfunded' AML group was 22 months (95% CI 11.7-24.9).

Patients in both groups who failed to complete more than 6 cycles of azacitidine also had a similar outcome (p=0.39), with a median survival of 5.7 months (95% CI 4.0-6.3) for patients with MDS/AML 20-30% blasts and 3.6 months (95% CI 2.2-5.1) for AML patients with > 30% blasts or relapsed/refractory disease. Reasons for patients not completing at least 6 cycles of azacitidine included progression of disease (25%), bacterial infections most commonly pneumonia (53%) and patient preference (7%).

CONCLUSION: A significant sub-population of AML patients with > 30% blasts or refractory/relapsed AML can achieve a meaningful survival benefit with the hypomethylating agent, azacitidine. A higher proportion of this AML patient population discontinued azacitidine as a result of infective complications. The provision of routine prophylactic antibiotics may enable more patients with AML to receive an adequate amount of azacitidine to achieve therapeutic benefit and warrants further investigation. Our results add to the growing body of 'real-world' evidence that supports healthcare funding agencies to provide coverage of azacitidine for patients with AML who in some countries at present do not fulfill government funding criteria.