Researchers examined data from several case-control studies published between 1979 and 1998 and found that a majority of them reported elevated risk for CBT with risk increasing up to 2.5 times for maternal exposures and up to 6.7 times for children's exposures.

The largest increase was a 12-fold increased risk for a type of tumor known as primitive neuroectodermal tumors (PNET), with maternal exposure to pigs.

Brain tumors are the most common solid tumor in children, but currently little is known about their causes, and only a small percentage of cases can be attributed to established risk factors.

Exposure to farm animals and pets have been considered as possible risk factors for childhood brain tumor (CBT) development since numerous factors associated with farm life, including bacteria, pesticides, solvents and some animal viruses, have been found to induce brain tumor formation in animals.

Some studies have found viral gene sequences in human brain tumors.

Additionally, epidemiological studies of brain tumors in adults have reported an increased risk among veterinarians and farmers.

Paediatric & Perinatal Epidemiology 2000; 14: 248-256