This summary briefly covers smoking as a primary risk factor for cancer, but the main focus is on the effect of smoking on cancer recurrence and diagnosis of a second primary cancer; patterns of quitting and continued smoking in cancer patients; and recommendations for cancer patients to quit smoking. Information on cancer prevention and quitting smoking in healthy people is readily available elsewhere. The information presented in this summary is related to smoking, rather than using other forms of tobacco, such as snuff or chewing tobacco.