Survival and response
As noted, the median PFS was modestly but significantly longer with pembrolizumab plus EP at the second interim analysis, the protocol-specified time for final PFS analysis. The estimated 12-months PFS rates were 13.6% with pembrolizumab plus EP and 3.1% with placebo plus EP.
The final analysis was planned to occur about 31 months after the start of the study or when 284 deaths had occurred, whichever was later. At the final analysis, the median PFS was 4.8 months in the pembrolizumab arm and 4.3 months in the placebo arm. The hazard ratio was 0.73 (95% confidence interval 0.60-0.88).
The 12-month OS rate was 45.1% in the pembrolizumab arm and 39.6% in the placebo arm. Respective 24-month OS rates were 22.5% and 11.2%.
Overall responses rates were 70.6% in the pembrolizumab arm and 61.8% in the placebo arm. There were four and two complete responses per arm, respectively.
Safety
Approximately 75% of patients in both arms experienced grade 3 or 4 adverse events.
Fatal adverse events occurred in 6.3% of patients in the pembrolizumab arm and 5.4% in the control arm. The rates of death attributed to study treatment were identical, at 2.7% in each arm.
Events leading to discontinuation occurred in 14.8% of patients who received pembrolizumab and 6.3% of patients who received placebo. Adverse events leading to all treatment discontinuation were similar, at 4% and 3.6%, respectively.
The most common adverse events were hematologic, which are common with EP chemotherapy and did not appear to be exacerbated by the addition of pembrolizumab. Aside from hematologic toxicities, most events were of grade 1 or 2 severity.
Immune-mediated adverse events of any kind occurred in 24.7% of patients in the pembrolizumab arm and 10.3% of those in the placebo arm. Grade 3 or 4 immune-mediated events occurred in 7.2% and 1.3%, respectively.
There were no deaths from immune-mediated reactions in the pembrolizumab arm, but one patient on placebo died from pneumonia.
Merck Sharp & Dohme supported the study. Dr. Rudin disclosed institutional research funding from Merck and a consulting or advisory role for other companies. Dr. Owonikoko disclosed a consulting/advisory role and institutional research funding from Merck and others, and he is a cofounder and stock owner in Cambium Oncology.
SOURCE: Rudin CM et al. ASCO 2020. Abstract 9001.