The present invention relates to methods for treating cancer in a patient comprising administering a PD-1 antagonist, e.g., an anti-PD-1 antibody or antigen binding fragment thereof (e.g. pembrolizumab), in specific amounts to the patient about every six weeks. In some embodiments, the amount of anti-PD-1 antibody or antigen binding fragment thereof is about 400 mg. In certain embodiments, the PD-1 antagonist is pembrolizumab, or an antigen binding fragment thereof. Also provided are compositions and kits comprising a dosage of an anti-PD-1 antibody, or antigen-binding fragment thereof, and uses thereof for treating cancer.