Mothers who developed diabetes while pregnant - what doctor’s call gestational diabetes - appear to have a lower risk of developing breast cancer later in life, a new study hints.

Different studies of the possible relationship between diabetes and breast cancer risk have yielded conflicting results, explain Dr. Dana E. Rollison from the H. Lee Moffitt Cancer Center and Research Institute in Tampa, Florida and colleagues, and none have studied diabetes-associated breast cancer risk specifically among Hispanic women.

Therefore, Rollison’s team investigated possible differences in the association between diabetes and breast cancer among Hispanic women and non-Hispanic white women in a case-control study.

The researchers identified 1,526 white women and 798 Hispanic women with breast cancer diagnosed between 1999 and 2004, and matched them with a similar number of cancer-free controls.

Diabetes overall and type 2 diabetes were not associated with breast cancer, the team reports, but there was a statistically significant inverse association between gestational diabetes and breast cancer. That is, women who had had gestational diabetes had 30 percent lower odds of having breast cancer.

The effect was stronger when gestational diabetes was diagnosed before age 35 years.

Gestational diabetes affects roughly 4 percent of all pregnant women. “Should the inverse association between gestational diabetes and breast cancer be observed in future studies,” the researchers conclude, “potential biologic explanations should be further investigated.”

SOURCE: American Journal of Epidemiology, February 15, 2008.