Mateos MV, et al. - In patients with relapsed or refractory multiple myeloma, pomalidomide and dexamethasone with or without pembrolizumab were assessed for effectiveness and safety in a randomized, open-label, phase 3 trial conducted at 97 medical centers across 11 countries (Australia, Canada, France, Germany, Israel, Italy, Japan, New Zealand, Norway, Spain, and US). Researchers report the results of an unplanned, ad-hoc interim investigation at the request of the FDA. Eligible patients were randomly allocated to the pembrolizumab plus pomalidomide and dexamethasone group or the pomalidomide and dexamethasone group at a 1:1 ratio. Serious adverse events occurred in 63% of patients in the pembrolizumab plus pomalidomide and dexamethasone group vs 46% of patients in the pomalidomide and dexamethasone group. Four treatment-related deaths occurred in the pembrolizumab plus pomalidomide and dexamethasone group; myocarditis and Stevens-Johnson syndrome were considered related to pembrolizumab. No treatment-related deaths were reported in the pomalidomide and dexamethasone group. An unfavorable benefit–risk profile of pembrolizumab plus pomalidomide and dexamethasone was found for patients with relapsed or refractory multiple myeloma in this unplanned, FDA-requested, interim analysis.