PRF1 and colorectal cancer: The first prognostic immune signature describing the functional orientation of the tumor immune microenvironment was established in colorectal cancer and was composed of genes involved in Th1 and cytotoxic T cell function, including interferon- γ (IFN-γ), granulysin (GNLY), perforin (PRF1), and granzymes (GZMs) (47).