"This two-fold increased risk went away when we looked only at women who breast-fed, " Ursin says.

NPR: Study: Breast-Feeding Decreases Cancer Risk

This made Dr. Geske Ursin and her colleagues wonder whether the hormonal changes associated with pregnancy and breast-feeding were somehow the reason.

NPR: Study: Breast-Feeding Decreases Cancer Risk

And earlier this week, Ursin reported further good news at a meeting of the American Association for Cancer Research in Los Angeles.

NPR: Study: Breast-Feeding Decreases Cancer Risk