Recent studies found that lifestyle, tobacco use, secondhand smoke exposure, several occupational exposures, treatment type received, duration of anticancer treatment after diagnosis, endogenous circulating levels of sex hormones, and expression and mutation rates of several related genes (including EGFR, KRAS, and P53) had differences between men and women, and that sex differences have important implications for lung cancer development, prognosis, and treatment preferences. This evidence concerns the gene KRAS and lung cancer.