Chao J, Fuchs CS, Shitara K, et al. - Among patients suffering from microsatellite instability–high (MSI-H) advanced gastric or gastroesophageal junction (G/GEJ) cancer, the antitumor activity of pembrolizumab therapy vs chemotherapy was examined irrespective of the line of therapy in which it was administered in this post hoc study of the phase 2 KEYNOTE-059 (third-line treatment or higher) single-arm trial and the phase 3 KEYNOTE-061 (second-line treatment) and KEYNOTE-062 (first-line treatment) randomized trials. Among patients analyzed in this post hoc study, not only prolonged overall and progression-free survival but also durable responses were conferred by treatment with pembrolizumab therapy alone or in combination with chemotherapy, compared with chemotherapy alone, in patients who had undergone two or more previous lines of therapy in KEYNOTE-059, one previous line of therapy in KEYNOTE-061, or no previous therapy in KEYNOTE-062. Based on observations in this study, experts suggest MSI-H status as a possible biomarker for pembrolizumab therapy in patients with advanced G/GEJ cancer irrespective of the line of therapy in which it was administered.