In 1998 the Food and Drug Administration mandated that certain foods be fortified with folic acid because it had been shown that folic acid supplementation for pregnant mothers, significantly reduced neural tube defects in babies (e.g. spina bifida).
A study at the Washington University in St. Louis suggests that this fortification may also have lead to lower cases of some cancers in the infants. To quote:
“Rates of Wilms tumor (WT), primitive neuroectodermal tumors (PNETs), and ependymomas were significantly lower postfortification”
Wilms tumors is the most common type of kidney cancer, and primitive neuroectodermal tumors (referred to as PNETs) are tumors that affect soft tissue and bone.
Read more here.