The disclosure provides a method for treating a subject afflicted with a tumor, e.g., lung cancer, having a high tumor mutation burden (TMB) status comprising administering to the subject an immunotherapy, e.g., an anti-PD-I antibody or antigen-binding portion thereof. The present disclosure also provides a method for identifying a subject suitable for an immunotherapy, e.g., a treatment with an anti-PD-I antibody or antigen-binding portion thereof, comprising measuring a TMB status of a biological sample of the subject. A high TMB status identifies the patient as suitable for treatment with an anti-PD-I antibody or antigen-binding portion thereof. The TMB status can be determined by sequencing nucleic acids in the tumor and identifying a genomic alteration, e.g., a somatic nonsynonymous mutation, in the sequenced nucleic acids.