Response Rates of Phase 2 and Phase 3 Trials of Decitabine (DAC) in Patients with Myelodysplastic Syndromes (MDS).

Background: MDS is characterized by ineffective hematopoiesis, resulting in cytopenias with dysplastic morphology of peripheral blood cells and bone marrow. Decitabine (Dacogen^™ DAC) is a cytosine analog that reverses aberrant DNA methylation, leading to re-expression of silenced tumor suppressor genes. Due to the requirement for DNA synthesis and subsequent demethylation, decitabine may require prolonged administration to achieve maximum benefit. Overall response rates (ORR) (CR+PR) from 1 pivotal Phase 3 (D-0007) and 3 supportive Phase 2 trials (91–01, 95–11 and 97–19) in patients with intermediate and high risk MDS receiving DAC are being presented.

Methods: The Phase 2 trials were open-label and single-arm, with a minimum of 4 treatment cycles and a maximum of 8 cycles, while the D-0007 was a 1:1 randomized comparison of DAC plus supportive care (SC) vs. SC alone, with a maximum of 10 cycles of therapy. The D-0007 study design dictated that patients be removed from therapy following 8 cycles of decitabine if CR was not achieved, and 6 cycles in the absence of PR. Patients who maintained a CR for 2 cycles were removed from therapy.

Results: A total of 271 unique patients were exposed to DAC in the studies (n= 89 in D-0007, n=29 in 91–01, n = 66 in 95–11, n = 87 in 97–19). Patients receiving DAC had similar demographics and disease characteristics in all trials. Responses were observed in all IPSS and FAB subgroups. The percent of patients classified as intermediate-2 and high risk (according to the International Prognostic Scoring System) in the Phase 3 trial was 69% vs. 72% in the Phase 2 trials. By intent-to-treat analysis, the ORRs were 45%, 26%, and 26% respectively, for the Phase 2 trials. These results were corroborated in the Phase 3 trial, where the response rates were evaluated according to the more robust International Working Group MDS criteria, following a blinded, centralized bone marrow review. The D-0007 overall response rate was 17% for DAC (9% CR, 8% PR) vs. 0% for SC (p<0.001). Responses were durable, lasting a median of 266 days. The 95–11 and 97–19 response rates were also centrally reviewed, while 91–01 responses were investigator-assessed. In the 91–01 trial, the ORR was 45% (28% CR, 17% PR) with a median duration of response of 217 days, the 95–11 ORR was 26% (21% CR, 5% PR) with a median duration of 250 days, and the 97–19 ORR was 26% (22% CR, 5% PR) with a median duration of 146 days. Hematologic improvement (HI) was also evaluated according to varied criteria in conjunction with the response rates in all 4 studies; 12 patients (13%) had HI in D-0007, 2 patients (7%) in 91–01, 8 patients (12%) in 95–11, and 13 patients (15%) in 97–19. The D-0007 trial design dictated that patients who maintained a CR for 2 cycles be removed from therapy. As a result, the median number of cycles delivered was 3, with only 48% of patients receiving ≥4 cycles. In the Phase 2 studies, the median number of cycles is clearly higher (median 4), with the majority of patients receiving at least 4 cycles and approximately one-third of patients receiving ≥6 cycles.

Conclusion: While response rates of ≥17% were demonstrated in these trials, the optimization of hypomethylating agents for maximum efficacy is very likely to include prolonged therapy, which may correlate with increases in response rate and duration.