Association of potential biomarkers with clinical outcomes in metastatic triple-negative breast cancer treated with pembrolizumab or chemotherapy.

In the randomized, phase 3 KEYNOTE-119 study, overall survival (OS) was not significantly improved with pembrolizumab 200 mg Q3W versus investigator's choice of chemotherapy in participants with previously treated metastatic TNBC. In this exploratory analysis, we evaluated associations of tumor-infiltrating lymphocytes (TILs), T-cell‒inflamed gene expression profile (TcellinfGEP), BRCA1/BRCA2 mutation (BRCAm) status, homologous recombination deficiency (HRD) status, and tumor mutational burden (TMB) with clinical outcomes. TIL level was associated with improved objective response rate (ORR), progression-free survival (PFS), and OS with pembrolizumab but not with chemotherapy or after adjusting for TcellinfGEP. Associations were also identified between TcellinfGEP and improved ORR, PFS, and OS with pembrolizumab. Participants with TMB ≥ 10 mut/Mb showed a trend toward increased benefit with pembrolizumab versus chemotherapy. No association was seen between BRCAm/HRD status and treatment response. These findings suggest a positive association between TILs, TcellinfGEP, and TMB with clinical outcomes in patients with metastatic TNBC receiving pembrolizumab. ClinicalTrials.gov Identifier: NCT02555657 (date of registration: September 18, 2015).