CHICAGO – In gastric and gastroesophageal junction (GEJ) cancers, positive for PD-L1, treatment with the PD-1 inhibitor pembrolizumab offered comparable survival with fewer side effects, according to results of a phase 3 randomized clinical trial.
The checkpoint inhibitor also demonstrated a clinically meaningful improvement in patients who had high levels of PD-L1 expression, with a 2-year survival rate of 39% versus 22% for patients receiving the standard chemotherapy, which consisted of a platinum and a fluoropyrimidine, according to Josep Tabernero, MD, PhD, lead author of the KEYNOTE-062 study.
By contrast, the study failed to demonstrate that pembrolizumab immunotherapy combined with that chemotherapy backbone was superior to chemotherapy alone on survival endpoints, said Dr. Tabernero, Head of the Medical Oncology Department at the Vall d’Hebron Barcelona University Hospital and Institute of Oncology, Spain.
“There are several factors we are evaluating,” Dr. Tabernero said here in a press conference at the annual meeting of the American Society of Clinical Oncology (ASCO). “We still have to do more studies to understand why, with this chemotherapy backbone, we don’t see a clear synergistic effect for superiority in overall survival.”
Nevertheless, these findings make pembrolizumab a “preferred treatment” for many patients, particularly in light of its “substantially improved safety profile” versus chemotherapy, said ASCO Senior Vice President and Chief Medical Officer Richard L. Schilsky, MD.
“What I take away from this study is that for patients with advanced gastric and gastroesophageal cancer, pembrolizumab should really in many cases replace chemotherapy as a first-line treatment for this population,” Dr. Schilsky said in a press conference. “It’s certainly not worse, and it may well be better.”
The KEYNOTE-062 study included 763 patients with HER2-negative, PD-L1-positive advanced gastric or GEJ cancers randomized to one of three arms: pembrolizumab alone for up to 35 cycles, pembrolizumab for up to 35 cycles plus chemotherapy, or placebo plus chemotherapy.
Pembrolizumab alone was not inferior compared to chemotherapy, with median overall survival rates of 10.5 and 11.1 months, respectively (HR, 0.91; 99.2% CI, 0.69-1.18), Dr. Tabernero reported.
Overall survival appeared to be prolonged in patients with high levels of PD-L1 expression, defined as a combined positive score (CPS) of 10 or greater. The median survival in that subgroup was 17.4 months for those receiving pembrolizumab, and just 10.8 months for chemotherapy. However, the design of the study precluded an analysis of statistical significance for this finding, according to Dr. Tabernero.
Looking at the overall study population, pembrolizumab plus chemotherapy did not improve survival versus chemotherapy alone, he added, reporting median overall survivals of 12.5 and 11.1 months, respectively (P = .046).
Subgroup analysis suggested that Asian patients derived particular benefit from pembrolizumab as compared to chemotherapy, though Dr. Tabernero cautioned against overinterpretation of the finding, saying that it could be due to biology, or could be a statistical anomaly.
Funding for the study came from Merck & Co., Inc. Dr. Tabernero reported disclosures related to Bayer, Boehringer Ingelheim, Lilly, MSD, Merck Serono, Novartis, Sanofi, and others.
SOURCE: Tabernero J, et al. ASCO 2019. Abstract .