Although no treatment-related deaths occurred in the pomalidomide/dexamethasone arm alone, 4 patient deaths were attributed to treatment of pembrolizumab-containing therapy, and in 2 cases, these were associated with myocarditis and Stevens-Johnsons syndrome. The serious adverse event rate was 63% and 46% in patients receiving treatment with and without the immune checkpoint inhibitor, respectively.

Estimated rates of 6-month PFS were 48% for patients receiving pembrolizumab-containing therapy, and 60% for those treated with pomalidomide/dexamethasone alone. Corresponding estimates of 6-month OS rates were 82% and 90%.

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Following the findings of early mortality in these analyses that were not specified in the clinical trial protocols, a data monitoring committee halted enrollment in both studies, and the studies were subsequently terminated by the FDA.

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1. Usmani SZ, Schjesvold F, Oriol A, et al.  Pembrolizumab plus lenalidomide and dexamethasone for patients with treatment-naive multiple myeloma (KEYNOTE-185): a randomised, open-label, phase 3 trial [published online July 18, 2019]. Lancet Haematol. doi: 10.1016/S2352-3026(19)30109-7

2. Mateos MV, Blacklock H, Schjesvold F, et al. Pembrolizumab plus pomalidomide and dexamethasone for patients with relapsed or refractory multiple myeloma (KEYNOTE-183): a randomised, open-label, phase 3 trial. Lancet Haematol. doi: 10.1016/S2352-3026(19)30110-3