Toxic Inheritance.

Fathers' Job May Mean Cancer for Kids

Exactly how cancer takes root in children remains much a mystery, despite broad investigations into the matter. Now a new study supports the idea that a father's occupation just before conception may play a role [EHP 109:193-198]. More specifically, the chemicals he is exposed to on the job may affect his children's health after birth, contributing to the development of nervous system tumors and, more rarely, leukemia--the two most common types of childhood cancer. The study, led by Maria Feychting of the Karolinksa Institute in Stockholm, Sweden, lends credence to the hypothesis that paternal occupational exposures may be important in the etiology of childhood cancer.

Thanks to the combination of Sweden's unique population registry and its high-quality national cancer registry, the researchers were able to follow more than 235,000 Swedish children from birth through their early teens. The team essentially tracked all children born to married couples after two censuses in the mid-1970s and early 1980s, comparing cancer cases with paternal occupational exposures extrapolated from census information. About 522 children developed cancer, including roughly 160 cases of nervous system cancers and 160 cases of leukemia.

For each occupation represented among the fathers, two experienced industrial hygienists calculated the probability of exposure to different agents, such as pesticides, heavy metals, and solvents. The team found that the risk of nervous system cancers more than doubled among children whose fathers were exposed to pesticides, solvents, or paint products. In fact, risk tripled for children of house and industrial painters. Risk of developing leukemia also doubled among children of woodworkers. Both findings reinforce earlier studies.

The study adds to the knowledge base about a possible association between pesticides and nervous system tumors in children. It also raises new questions about some specific exposures. For instance, the study found that the risk of leukemia increased fourfold for children whose fathers were among a small sample of sheet metal workers. Curiously, leukemia risk doubled for children with fathers in government legislature and administration work, a link supported by previous studies. Some of the findings, however, contradict earlier studies. For instance, with regard to childhood leukemia, the team found no link between paternal exposures to pesticides and paint, as others had reported previously.

Feychting and her colleagues propose two causal mechanisms for the associations. First, the child may be exposed via the placenta to carcinogenic substances carried into the home by the father. Second, even before conception, the occupational exposure may cause a genetic change in the father's sperm that affects the child's cancer susceptibility. The latter is supported by earlier studies.

Aside from its sheer size, the investigation is notable as one of the first cohort studies of its kind to collect information before cancers occur in children, according to Feychting. This ensures that exposure classification is made independent of disease status, she explains. By contrast, in some prior case--control studies, recall bias potentially clouded the results because exposure information was often collected after the manifestation of disease. The study's design also eliminated the possibility of selection bias because the exposure data were derived from censuses that captured information for more than 99% of the population.

However, the study's exposure assessment weakens the results somewhat, Feychting acknowledges, because exposures were estimated based only on each father's occupational title and type of industry. Although guaranteeing that any exposure misclassification is unrelated to disease, the method leaves little room for analysis of dose--response patterns and opens the door to inaccuracies. For example, some fathers may have changed jobs at the actual time of conception. The team is now undertaking a follow-up case--control study of childhood nervous system tumors to tease out paternal exposures before birth from those during pregnancy or after birth by interviewing parents about exposures at work and home.