Elevated PD-L1 Expression and Microsatellite Instability in Elderly Patients With Gastric Cancer

Immunotherapy in combination with chemotherapy is the current treatment of choice for frontline programmed cell death ligand 1 (PD-L1)-positive gastric cancer. However, the best treatment strategy remains an unmet medical need for elderly or fragile patients with gastric cancer. Previous studies have revealed that PD-L1 expression, Epstein-Barr virus association, and microsatellite instability-high (MSI-H) are the potential predictive biomarkers for immunotherapy use in gastric cancer. In this study, we showed that PD-L1 expression, tumor mutation burden, and the proportion of MSI-H were significantly elevated in elderly patients with gastric cancer who were older than 70 years compared with patients younger than 70 years from analysis of The Cancer Genome Atlas gastric adenocarcinoma cohort [≥70/<70: MSI-H: 26.8%/15.0%, P=0.003; tumor mutation burden: 6.7/5.1 Mut/Mb, P=0.0004; PD-L1 mRNA: 5.6/3.9 counts per million mapped reads, P=0.005]. In our real-world study, 416 gastric cancer patients were analyzed and showed similar results (≥70/<70: MSI-H: 12.5%/6.6%, P=0.041; combined positive score ≥1: 38.1%/21.5%, P<0.001). We also evaluated 16 elderly patients with gastric cancer treated with immunotherapy and revealed an objective response of 43.8%, a median overall survival of 14.8 months, and a median progression-free survival of 7.0 months. Our research showed that a durable clinical response could be expected when treating elderly patients with gastric cancer with immunotherapy, and this approach is worth further study.