Epidemiological study has been performed on the relation between three cancers and five genes under the influence of tobacco smoking. The three cancers are stomach cancer, colorectal cancer and urothelial cancer, while five genes are glutathione S-transferase Ml, Tl, PI and N-acetyltransferase 1 and 2. We clarify the genetic polymorphisms increase the susceptibility to the cancers, especially by smoking tobacco.
