Sun Young Rha, MD, PhD, Yonsei Cancer Center, Seoul, South Korea, talks on unanswered questions surrounding the treatment of gastric cancer (GC). Despite positive data for immunotherapy in patients with GC, the improvement of clinical efficacy is limited. Patients that do demonstrate a survival benefit are those that can be placed in particular subgroups. So, the issue in question is selecting the correct biomarker to enable selection of the appropriate subgroup of patients to treat with suitable targeted immunotherapies, such as pembrolizumab. Dr Rha explains that in the near future we will be able to decipher the appropriate subgroup of patients who will benefit from immunotherapy as a mono- or combinational therapy. In patients who are HER2-negative, the addition of an immune checkpoint inhibitor to chemotherapy influences survival. This was demonstrated in the KEYNOTE-A18 (NCT04221945) clinical trial which showed that chemoradiotherapy with pembrolizumab benefited patients with GC in the first-line setting. Immunotherapy may also be important in the preoperative setting to improve survival in addition to chemotherapy, which is currently being investigated in the Phase III KEYNOTE-585 (NCT03221426) clinical trial. This interview took place at the American Society of Clinical Oncology (ASCO) Gastrointestinal Cancers Symposium.