Environmental causes of cancer in childhood.

Although it is commonly said that only a small proportion of childhood cancers are caused by environmental exposures, much has been learned about exogenous carcinogens through study of their effects or noneffects in children: 1. Ionizing radiation poses some risk no matter how small the dose. 2. Concepts about the viral etiology of cancer have had to be adapted to fit observations in children concerning candidate viruses. 3. Transplacental chemical carcinogenesis has become a reality and poses an increasing threat as chemical pollution worsens. 4. Questions have been raised about the risk of breast feeding in (at present) rare instances when the mother has been heavily exposed to chemicals that are excreted in the fat of breast milk. 5. A few drugs administered to children induce cancers within the pediatric age-span. The pediatrician must take action not only against exogenous agents that induce cancer while the patient is under his care, but also against exposures that begin in utero and lie latent or accumulate throughout life to give rise to cancers in the years or decades ahead. There is much more to carcinogenesis than the effects of the environment. Important information has been gained about the origins of cancer and about human biology in general through studies of children who are unusually susceptible to certain forms of neoplasia. Knowing the mechanisms involved may lead to new modes of treatment, to screening tests for environmental carcinogens or to methods for detecting cancer early enough for treatment to be life-saving.