Gene May Offer Protection From Breast Cancer, Study Suggests : Health: Research on mice indicates that process kicks into high gear during pregnancy. It may also be helping young mothers.

Pregnancy kicks an anti-cancer gene into high gear in the breasts of mice, a study says, offering a possible clue to why women run a lower risk of breast cancer if they give birth early in life.

If that notion is correct, it might lead to a risk-lowering treatment for women in general.

Studies show that women who give birth at age 18 run about one-half to one-third the lifetime breast cancer risk of childless women, said researcher Lewis Chodosh of the University of Pennsylvania School of Medicine. The benefit declines the longer a woman waits to have a baby, and by age 30 it is gone.

The mouse study, by Chodosh and others, suggests the possibility that pregnancy stimulates an anti-cancer gene in women that stays overactive long after the child is born, maybe even permanently.

The human gene is called BRCA1. It is best known for raising the risk of breast cancer when it is defective and unable to provide its normal protection.

The mouse study was published in the September issue of the journal Nature Genetics. Researchers found that the rodent version of BRCA1 becomes unusually active in mouse breasts early in pregnancy and continues that way until birth. After that, its activity declines but remains above levels seen in virgin mice for at least four weeks, Chodosh said.

Pregnancy is a time of increased breast cancer risk, Chodosh said, and the overactivity of the gene may be a protective reaction.

The observation that the gene remains somewhat overactive after pregnancy raises the possibility that it plays some role in the long-term anti-cancer benefit of having a child, he said.

But he stressed that there is no proof of that idea. And even if the gene does play a role, it’s not clear whether it could be used to provide long-term breast cancer protection in women, he said.

The researchers also found that the mouse gene could be turned on by a combination of estrogen and progesterone.