A method for analyzing cell free DNA (cfDNA) from the bloodstream of a cancer patient is provided. In some embodiments, the method may comprise sequencing at least part of the coding sequences of TP53 and KRAS in a sample of the cfDNA, analyzing the sequences to identify nucleotide transversions in the coding sequences of the genes, relative to reference sequences of the genes. In some embodiments, the method may comprise counting the total number of identified nucleotide transversions. The presence of nucleotide transversions indicates that the patient will be more responsive to the immune checkpoint inhibitor, whereas a decreased number of transversions or no transversios indicates that the patient will be less responsive to the immune checkpoint inhibitor.
