KEYNOTE-859 STUDY

The KEYNOTE-859 study investigated the efficacy of pembrolizumab combined with chemotherapy versus placebo plus chemotherapy in patients with HER2-negative gastric/gastroesophageal junction (G/GEJ) cancer. With a median follow-up of 41.6 months, the study demonstrated significant improvements in overall survival (OS), progression-free survival (PFS), and overall response rate (ORR) for the pembrolizumab + chemo group. Specifically, the median OS was 12.9 months compared to 11.5 months for the placebo group (HR, 0.79). Patients with a PD-L1 combined positive score (CPS) ≥1 and ≥10 also showed significant benefits in OS and PFS with pembrolizumab + chemo. Treatment-related adverse events were slightly higher in the pembrolizumab group. These findings support the use of pembrolizumab combined with chemotherapy as a first-line treatment for patients with locally advanced or metastatic HER2-negative G/GEJ adenocarcinoma, showing sustained efficacy and manageable safety profiles over extended follow-up.