Pharmacokinetics is the study of the time course of drug concentration in the body. Several monoclonal antibodies are now in clinical use for digestive cancer therapy and several are emerging, especially immune checkpoint inhibitors. Pharmacokinetics of these drugs shows a large interindividual variability which can be explained by different factors. In some cases, tumor burden may influence pharmacokinetics: when tumor burden increases, exposure of monoclonal antibody decreases. There is also a relationship between drug exposure and clinical efficacy. This can be used to identify appropriate dose regimen at the individual level.