Induction refers to the earliest genetic change induced by a carcinogen. Promotion refers to cell growth induction that fixes and then further alters the genetic abnormality. Both may be necessary to create a cancer. Since prolonged exposure is one of the necessary ingredients to both induction and promotion, prevention of cancer in the elderly must begin before people become old. The best evidence strongly recommends avoiding smoking, overuse of alcohol, and exposure to known toxic chemicals.
Hormonal exposure is implicated in the development of breast, prostate, and uterine cancers.
Studies have been inconsistent as to whether exogenous estrogen exposure increases breast cancer risk, but the relative risk is probably in the range of 1.3. Early menarche, late menopause, and late or no pregnancies are confirmed risk factors. Drugs may also reduce the risk of some cancers. Tamoxifen has recently been approved for breast cancer prevention. Retinoids may be helpful in reducing the risk of new primary squamous cell cancers in persons with previous such cancers related to tobacco use.