Preliminary Results from a Phase II Study of the Combination of Azacitidine and Pembrolizumab in Patients with Higher-Risk Myelodysplastic Syndrome

Background: The survival of patients with myelodysplastic syndrome (MDS) after hypomethylating agent (HMA) failure is poor at about 4 to 6 months. The exposure of CD34 positive cells from patients with MDS to HMA has been shown to result in increased expression of PD-1 and PD-L1, with a sequential increase in the expression of PD-1 and PD-L1 particularly in patients that have failed HMA (Yang H, Leukemia 2014). Pembrolizumab is a humanized monoclonal antibody targeting PD-1, thus blocking its interaction with ligands PD-L1 and PD-L2, that has been FDA-approved for certain solid tumors. Consequently, we designed an ongoing phase II clinical trial to evaluate the safety and clinical activity of the combination of azacitidine and pembrolizumab in patients with higher-risk MDS. Methods: Adult patients with intermediate-1 or higher disease by the International Prognostic Scoring System (IPSS) were eligible for the study. Patients were divided into two cohorts: those who had not received prior therapy and those who had not responded to, progressed on, or relapsed after HMA therapy, with a goal enrollment of 20 patients per cohort. Patients received azacitidine 75 mg/m2 IV or SQ daily for 7 days on a 28-day cycle and pembrolizumab 200 mg IV starting on cycle 1 day 1 and every 3 weeks thereafter independent of azacitidine dosing schedule. The endpoints were overall response rate and safety. Patients were discontinued from the clinical trial if there was disease progression, unacceptable adverse experiences, intercurrent illness preventing further administration of study treatment, confirmed positive serum pregnancy test, noncompliance, loss to follow-up, completion of 24 months of uninterrupted treatment with pembrolizumab or 35 administrations of the study medication (whichever occurred later), lack of efficacy, or any other reason leading to the investigator's decision for withdrawal. Clinical trial information: NCT03094637. Results: At data cut-off (July 2018), 18 patients have been treated with azacitidine and pembrolizumab with a median follow-up time of 16 weeks and 9 patients continuing on treatment in cycles 1-6. Twelve patients were enrolled in the HMA failure cohort and 6 patients in the previously untreated MDS cohort. Of the 12 patients evaluable for response, 7 were in the HMA failure cohort and 5 in the previously untreated MDS cohort. In the HMA failure cohort, 1 patient achieved CR, 1 patient demonstrated hematological improvement with mCR or CRi,