Increased exposure to traffic was linked to increases in these rare types of childhood cancer, according to research presented by UCLA scientists at the annual meeting of the American Association for Cancer Research.

The identified cancers were acute lymphoblastic leukemia (white blood cell cancer), germ-cell tumors (cancers of the testicles, ovaries and other organs) and retinoblastoma (eye cancer), particularly bilateral retinoblastoma, in which both eyes are affected.

Looking at data on 3,950 children enrolled in the California Cancer Registry, pollution exposure was estimated for the area around each child’s home for each trimester of their mother’s pregnancy and during their first year of life. Estimates included information on gasoline and diesel vehicles within a 1,500-meter radius buffer, traffic volumes, roadway geometry, vehicle emission rates and weather. Cancer risk was estimated using a statistical analysis known as unconditional logistic regression.

When comparing data between pregnancy trimesters and the first year of life, no particular period stood out as a higher-exposure time. As such, it is difficult to determine if one period of exposure was more dangerous than any other, according to researchers. They team did note that, due to the rarity of the specific illnesses, findings need to be replicated in further studies.