- The immune checkpoint inhibitor pembrolizumab, when added to chemotherapy, almost doubled PFS in patients with metastatic triple-negative breast cancer (mTNBC) in the phase 3 KEYNOTE-355 trial.
Why this matters
- Previous trials found that pembrolizumab monotherapy improved PFS in mTNBC.
- This is the first study of combination therapy.
- Findings suggest that pembrolizumab should be added to standard chemotherapy for mTNBC, but only in patients with PD-L1 expression scores ≥10.
- Randomized, placebo-controlled, double-blind, phase 3 trial of chemotherapy (taxane or gemcitabine-carboplatin) with or without pembrolizumab (combination group of pembrolizumab+chemotherapy) vs placebo group (placebo+chemotherapy) (n=847).
- Each group was analyzed in 3 overlapping subgroups: patients with PD-L1 CPS ≥10, patients with PD-L1 CPS ≥1, and the intention-to-treat population.
- Patients with previously untreated locally recurrent inoperable TNBC were also included.
- Funding: None disclosed.
- Median follow-up was 25.9 months in the combination group and 26.3 months in the placebo group.
- Patients with CPS ≥10: median PFS was 9.7 months in the combination group vs 5.6 months in the placebo group.
- HR, 0.65 (95% CI, 0.49-0.86).
- Patients with CPS ≥1: median PFS was 7.6 months in the combination group and 5.6 months in the placebo group.
- HR, 0.74 (95% CI, 0.61-0.90; P value not significant).
- Subgroups were underpowered.