As in many cancers, immunotherapy is strengthening its position day by day in the treatment of gastrointestinal system cancers, with promising results of new studies. In this review, the current treatment recommendations will be shared with the results of immunotherapy studies performed in the esophageal, gastroesophageal junction (GEJ), gastric, and colorectal cancers. Esophagus/Gastroesophageal Junction and Gastric Cancers CheckMate-577, a study conducted in stage II–III esophageal (squamous or adenocancer) and GEJ cancers, was presented at ESMO2020, and for the first time, immunotherapy was included in the guidelines for early stage gastrointestinal system cancers. In this study, it was shown that a twofold disease-free survival advantage was achieved with the use of 1-year nivolumab (NIVO) treatment in the adjuvant setting for patients who had residual disease after preoperative chemoradiotherapy followed by surgery. The proportion of patients with Programmed death-ligand 1 (PD-L1) expression < 1% was 70%. Based on the findings of this study, adjuvant NIVO is recommended regardless of PD-L1 expression.[1] The ATTRACTION-3 study was a multicenter, randomized, openlabel, and phase 3 study. In this study, the effectiveness of NIVO versus taxane chemotherapy (CT) was investigated in patients with advanced esophageal cancer (squamous) who were refractory or intolerant to previous CT. The primary endpoint of the study was overall survival (OS). NIVO was effective in terms of OS in all patient groups; however, in the subgroup analysis, the largest benefit was observed in the patients with PD-L1 expression >1% [(NIVO vs. CT; mOS; 10.9 vs. 8.1 months, hazard ratio (HR) (95% confidence interval (CI) = 0.69 (0.51–0.94)].[2] Relying on the efficacy and safety data of this study, Food and Drug Administration (FDA) and European Medicines Agency approved NIVO in patients with unresectable, recurrent, or metastatic squamous subtype esophageal cancer who previously received fluoropyrimidine and platinum-based CT. At ASCO-GI 2020, the 3-year survival results of the ATTRACTION-2 study were announced. In this phase 3 study by Chen et al. which included 49 centers from Asian countries, the effectiveness of NIVO versus placebo was investigated. Patients with unresectable, advanced, or recurrent gastric and GEJ adenocarcinoma who received 2 or more lines of CT regimens were included; the primary endpoint was OS. At 3-year follow-up, the median OS was 5.26 months in the NIVO group versus 4.12 months in the placebo, with HR (95% CI) = 0.62 (0.50–0.75), p<0.0001. In patients