Specifically, smoking before menopause and especially before giving birth may be linked to a modest increase in breast-cancer risk. Researchers at Brigham and Woman's Hospital and Harvard Medical School analyzed records of 111,140 female active smokers from 1976 to 2006 and 36,017 female passive (secondhand) smokers from 1982 to 2006.
They found a total of 8,772 cases of breast cancer developed during the follow-up period, which correlated with a higher quantity of current and past smoking, smoking longer and younger age at smoking initiation, among other factors.
The authors said smoking before menopause was "positively associated with breast cancer risk," whereas smoking after menopause might be tied to lower breast cancer risk because of cigarettes' antiestrogenic effect.
Never smoking and passive (secondhand) smoking were not associated with breast cancer risk.
The authors conclude that although an elevated risk for light smokers and moderate smokers was not apparent, "heavy smokers who started smoking early in life, smoked for a long duration and smoked a high quantity" were at the highest risk of breast cancer among those studied.
Smoking has also been linked to cancers of the throat, mouth, nasal cavity, esophagus, stomach, pancreas, kidney, bladder, and cervix, and acute myeloid leukemia, according to cancer.gov.