Although pembrolizumab as second- or third-line treatment of patients with metastatic triple negative breast cancer (TNBC) did not improve overall survival (OS) compared with chemotherapy in all patients or in those with all PD-L1-positive tumours in the Asia-Pacific subgroup of a phase III KEYNOTE-119 study, the immune checkpoint inhibitor therapy did show some promise in one subgroup with highest PD-L1 expression, according to findings presented at the ESMO Asia Virtual Congress 2020, held from 20 to 22 November 2020.
Pembrolizumab activity was seen to increase in cohorts of patients with higher PD-L1 combined positive score (CPS) and did improve OS over chemotherapy for the exploratory endpoint in the cohort of patients with CPS ≥20.
According to Professor Seock-Ah Im from Seoul National University Hospital in Seoul, Republic of Korea, chemotherapy is the standard of care for metastatic TNBC, but the short duration of response and considerable toxicities have prompted the investigation for immune checkpoint inhibitor pembrolizumab.
Professor Im presented findings on behalf of colleagues from the Asia-Pacific subpopulation of the randomised, open-label, phase III KEYNOTE-119 (NCT02555657) study comparing the efficacy and safety of pembrolizumab versus chemotherapy as second- or third-line treatment for patients with metastatic TNBC.
Of note, a similar pattern was demonstrated in the entire population of KEYNOTE-119 wherein pembrolizumab did not significantly improve OS over chemotherapy in patients with CPS ≥10 (p = 0.0574) or CPS ≥1 (p = 0.0728).1
KEYNOTE-119 enrolled 622 patients with stage IV/M1 TNBC and disease progression following 1-2 prior treatments that included anthracycline and/or taxane. Stratification was by PD-L1 status (positive, defined as CPS ≥1, versus negative, defined as CPS <1) and whether patients had a history of (neo)adjuvant treatment versus de novo metastatic disease.
The patients were randomly assigned equally to pembrolizumab at 200 mg i.v. every three weeks or physicians’ choice of single agent chemotherapy with capecitabine, eribulin, gemcitabine, or vinorelbine. Response was assessed by CT/MRI every 9 weeks during the first year and every 12 weeks thereafter.
The primary endpoints of the trial included OS in patients overall and in those with CPS ≥10, and CPS ≥1; secondary endpoints included progression-free survival (PFS) as well as the objective response rate (ORR) and duration of response (DoR) per RECIST v1.1. The study included exploratory endpoints of OS, PFS, ORR, and DoR in patients with PD-L1-positive tumours and CPS ≥20.
Pembrolizumab improved OS compared with chemotherapy only in patients with the highest PD-L1 expression
In the Asia-Pacific group 83 patients received pembrolizumab and 98 were treated with chemotherapy. The median time from randomisation to data cut-off was 31.4 and 32.8 months in the respective treatment arms.
Approximately half of the Asia-Pacific patients had PD-L1-positive tumours: 103 (57%) patients had CPS ≥1, 46 (25%) had CPS ≥10 and 24 (13%) patients had CPS ≥20.
In Asia-Pacific patients overall, the median OS was 11.6 months with pembrolizumab compared to 13.8 months with chemotherapy. In patients with CPS ≥1 median OS was 12.2 months with pembrolizumab versus 15.1 months with chemotherapy and the CPS ≥10 cohort showed median OS of 15.6 months versus 17.8 months, respectively.
However, in the exploratory endpoint cohort patients with CPS ≥20 demonstrated median OS of 23.5 months with pembrolizumab versus 19.1 months with chemotherapy.
Median PFS in Asia-Pacific patients overall was 2.1 months with pembrolizumab compared to 4.1 months with chemotherapy.
The ORR was 12% with pembrolizumab with 10 patients achieving response compared to 13 (13% ORR) patients on chemotherapy. Three patients in each arm demonstrated complete response. Interestingly, ORR increased in the pembrolizumab group with increasing PD-L1 enrichment. The ORR was 18.2 % for CPS ≥10 and 25% for CPS ≥20 in Asia-Pacific subpopulation.
In responding patients, the response was more durable with pembrolizumab; median DoR was 13.4 months with pembrolizumab and 8.4 months with chemotherapy.
Grade 3/4 treatment related adverse events (TRAEs) occurred in 16% and 45% of patients receiving pembrolizumab and chemotherapy, respectively. No deaths due to TRAEs occurred.
The authors noted that the results from the Asia-Pacific subpopulation were consistent with the global KEYNOTE-119 population.
Pembrolizumab did not show improved OS compared with chemotherapy in the Asia-Pacific subpopulation. However, they pointed out that an ad hoc analysis of patients with CPS ≥20 showed a numeric improvement in OS with pembrolizumab versus chemotherapy. Additionally, DoR for all patients was numerically higher with pembrolizumab, which was well tolerated compared with chemotherapy.
KEYNOTE-119 was funded by Merck Sharp & Dohme Corp., a subsidiary of Merck & Co., Inc., Kenilworth, NJ, USA.
- LBA 21 - European Society for Medical Oncology (ESMO) Congress 2019.
44O – Im S-A, Cortes J, Lipatov O, et al. Pembrolizumab (pembro) vs Chemotherapy (chemo) for Previously Treated Metastatic Triple-Negative Breast Cancer (mTNBC): KEYNOTE-119 Asia-Pacific Subpopulation. ESMO Asia Virtual Congress 2020 (20 to 22 November).