Smoking appears to alter gene expression in lung cells. The proteins produced by the bronchial cells of smokers show increased synthesis of genes, which can eventually evolve into cancer (become carcinogenic). It appears that depending on how these genes are configured, they can control cancer development, cancer suppression, or airway inflammation and varies according to the number of years a person spent smoking. The good news is that two years after a person stops smoking, his/her gene expression levels begin to resemble those of people who have never smoked.