A Phase II Study of Anti PD-1 Antibody Pembrolizumab, Pomalidomide and Dexamethasone in Patients with Relapsed/Refractory Multiple Myeloma (RRMM)

Abstract BACKGROUND Several recent studies have linked the interactions of programmed death 1 (PD-1) receptor and its ligand (PD-L1) to immunologic control of MM. Expression of PD-L1 on myeloma cells and the abundance of PD-1 on various bone marrow microenvironment components contribute to tumor-mediated immune suppression. We hypothesized that pembrolizumab, a PD-1-blocking antibody, will activate myeloma specific cytotoxic T cells that can be enhanced by pomalidomide in RRMM patients to induce clinical responses. METHODS In this ongoing single arm, phase II study, 24 patients with RRMM received 28-day cycles of pembrolizumab (at a dose of 200 mg IV) every 2 weeks (in a run off phase, first 6 patients received 200 mg IV every 4 weeks) plus pomalidomide (4 mg daily x 21 days) and dexamethasone 40 mg weekly. Study objectives were measurements of safety and efficacy and assessment of the PD-1 and PD-L1 protein expression in bone marrow samples. RESULTS The median age was 65 years (range: 41-75); 35% were African American and 71% were men. Of the 24 patients, 75% had prior autologous transplantation and 96% were refractory to last therapy. All patients had received both IMids and Proteosome inhibitors; 75% were double refractory to both IMids and Proteosome inhibitors and additional 21% were refractory to lenalidomide alone. Patients had received a median of 3 lines of prior therapy (range: 1-6). The median time from MM diagnosis to study entry was 4 years (range: 1.2-15). All patients had abnormal cytogenetics: most common were 1q+ (72%) and high-risk FISH (40%) [del 17p, t(4:14) and/or t(14:16)]. There were no infusion-related reactions. Hematologic toxicities (≥ grade 3) were neutropenia (29%), lymphopenia (17%) and thrombocytopenia (8%). Non-hematologic adverse events included (Grade ≤2; ≥3): fatigue (n=12; 1), constipation (n=10; 0), dyspnea (n=9; 2), itching (n=6; 0), muscle spasms (n=6; 0), infection (n=4; 3), hyperglycemia (n=5; 0), edema (n= 4; 0), fever (n=3; 0), palpitation (n=2; 1), rash (n=3; 1) and hypotension (n=3; 0). Events of clinical significance, autoimmune mediated, included hypothyroidism (n=2), transaminitis (n=2), and pneumonitis (n=1). Four patients had pomalidomide dose reductions due to rash, neutropenia, palpitations and fatigue. Two patients died; one after cycle 1 (progressive disease) and one during cycle 2 (sepsis). Objective responses (modified IMWG criteria) were observed in 11 of 22 evaluable patients (50%) including: near complete response (n=3), very good partial response (n=2), partial response (n=6); additionally, 3 patients had minimal response, 6 had stable disease and 2 progressed. At a median follow up of 16 weeks; 17 of 22 patients continued on the study. Reasons for discontinuation included disease progression (n= 4) and protocol violation (n=1). Analysis of pretreatment and post-treatment tumor specimens for PD-1 and PD-L1 is in progress. CONCLUSIONS Pembrolizumab in combination with pomalidomide and dexamethasone has promising therapeutic activity and an acceptable safety profile in heavily treated RRMM patients. ClinicalTrials.gov number, NCT02289222. Disclosures Off Label Use: Pembrolizumab.