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.

References

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