Metastatic TNBC: pembrolizumab in combo with chemo increases PFS in KEYNOTE-355

  • Cortes J & al.
  • Lancet
  • 5 Dec 2020

  • curated by Miriam Davis, PhD
  • Univadis Clinical Summaries
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Takeaway

  • 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.

Study design

  • 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.

Key results

  • 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).

Limitations

  • Subgroups were underpowered.