Individuals transplacentally exposed to maternal smoking may be at increased cancer risk in adult life.

Studies which provide evidence suggesting that cancer could result from transplacental exposure to maternal smoking include animal experiments showing that: (1) compounds present in tobacco smoke and cigarette smoke condensate itself are active transplacental carcinogens; (2) the fetus has greater sensitivity to some carcinogens than the adult, so that estimates of doses necessary for transplacental carcinogenesis cannot be accurately predicted from effects in adults; (3) carcinogens administered transplacentally can increase sensitivity to later carcinogenic exposures; and (4) many (at lower doses probably most) tumours resulting from transplacental exposure are not evident until adulthood and their morphology and sites do not differ from those of spontaneously occurring tumours. Studies in man have shown that components of tobacco smoke can reach the fetus and that human fetal tissues are capable of activating carcinogens similar to those in tobacco smoke. These findings suggest that conditions causing transplacental carcinogenesis in animals may be duplicated in man by prenatal exposure to maternal smoking, and that resulting tumours could occur in adulthood. In view of the widespread prevalence of smoking during pregnancy, epidemiological studies of cancer in adults should investigate the possible role played by maternal smoking in increasing cancer risk.