Duke Scientists Propose Possible Link Between Chemicals, Childhood Brain Cancer
DURHAM, N.C. – An analysis of medical records from 1,200 children who developed an aggressively malignant brain tumor called medulloblastoma has shown they are more likely to have been born in the late summer and early fall. The finding has prompted researchers to speculate that prenatal environmental exposures to chemicals could contribute to this cancer, whose causes remains largely unknown. They said their findings emphasize the need for additional studies into the environmental origins of medulloblastoma.
The researchers from Duke University Medical Center and the Nicholas School of the Environment and Earth Sciences at Duke said that seasonal variations in the use of pesticides, fungicides, other water pollutants and antihistamines could expose fetuses to these compounds during critical periods of brain development.
"Children born in the fall would have been conceived the previous winter, and major fetal development would occur during the spring," said Edward Halperin, M.D., vice dean of the school of medicine and a radiation oncologist at Duke. "Environmental events that occur during the spring more often than other times of the year might explain the differences."
Halperin and his Duke colleagues Marie Lynn Miranda, Ph.D., Dorothy Watson, Stephen George, Ph.D., and Matthew Stanberry published results of their study in the latest issue of Archives of Environmental Health, published April 1, 2005 but dated January, 2004. The research was supported by a Cancer Research Grant from the North Carolina Ladies Auxiliary to the Veterans of Foreign Wars of the United States.
Studies from Norway and Japan have also found a higher incidence of medulloblastoma among fall births, and several epidemiologic studies have shown correlations between pesticide exposure and the risk of childhood brain tumors, said Halperin.
Other reported associations between childhood brain tumors and fetal environmental exposures include the father's exposure to pesticides on the job and household use of chemical pest strips and pesticide aerosol bombs, said Halperin. Moreover, another study from Norway indicated that parents who worked in agriculture and who had significant pesticide exposure produced a statistically greater number of children with brain tumors who were born between April and June.
"The cerebellum undergoes rapid growth at certain periods of prenatal and postnatal development," said Halperin. "Environmental exposures could increase the risk of brain tumor, and our study provides some evidence that this may be the case."
In the Duke study, Halperin, Miranda and colleagues studied records of approximately 1,200 children with medulloblastoma between 1974 and 1999. The records were taken from the Duke Comprehensive Cancer Center, the North Carolina Central Cancer Registry, and the California Surveillance, Epidemiology and End Results data (SEER), drawn from the national SEER registry.
Medulloblastoma patients from Duke and North Carolina showed a higher rate of autumn births, particularly September and November. Their rates of fall births were nearly double in autumn – 44 percent -- compared to births in winter (23 percent) and spring (22 percent), the study showed. The children from California showed a lesser, but still significant, increase of medulloblastoma in autumn births. The national sampling, however, did not show a strong seasonal correlation, theoretically because it is difficult to account for variations in environmental exposure from one state to another, said the researchers.
"Seasonal phenomena vary in time of onset from one geographic or climatic region to another," said Halperin. "If we take a child born on September 15 in North Carolina, then the average date of conception would be December 23. The period of cerebellar development in the fetus – between eight and sixteen weeks – would correspond to February 17 to April 14 – late winter and early spring."
In North Carolina, this period is a time of higher environmental exposure to pesticides, herbicides, and fungicides -- either by direct exposure, atmospheric pollution, or water supply contamination by run-off, said Halperin. Pregnant women may also take products designed to treat allergic rhinitis during this season.
While direct links between medulloblastoma and chemicals in the environment have not been proven, there is enough evidence of an association for researchers to study the effects more thoroughly, the researchers said.
Still, the causes of medulloblastoma remain largely unknown, primarily because there so few cases of the disease, Halperin said. Medulloblastoma usually occurs in children between the ages of three and eight. This type of brain tumor comprises about 20 percent of all childhood brain tumors. It usually forms in the cerebellum, which is at the lower back of the brain.