The present invention provides therapeutic, diagnostic, and prognostic methods for cancer. The invention provides methods of treating a cancer, methods of determining whether an individual having a cancer is likely to respond to a treatment including an immune checkpoint inhibitor (e.g., a PD-L1 axis binding antagonist), methods of predicting responsiveness of an individual having a cancer to a treatment including an immune checkpoint inhibitor (e.g., a PD-L1 axis binding antagonist), methods of selecting a therapy for an individual having a cancer, methods of providing a prognosis for an individual having a cancer, and methods of monitoring a response of an individual having a cancer, based on a blood tumor mutational burden (bTMB) score or a maximum somatic allele frequency (MSAF) from a sample (e.g., a whole blood sample, a plasma sample, a serum sample, or a combination thereof) from the individual.