Scientists have found out why women who have a baby when they are relatively young have a lower risk of developing breast cancer. They have identified a substance produced naturally in the body that protects against the disease. Hormones released during pregnancy trigger the changes in the breast tissue of young women. The research raises the possibility of one day developing a pill that could protect against breast cancer.
In experiments, rats and mice given doses of natural hormones that mimic pregnancy were protected against breast cancer. When the animals were injected with a known carcinogen, they did not develop as many mammary tumours as expected. The research was carried out by a team at Baylor College of Medicine, Houston, Texas, US.
About 10% of women in the West will develop breast cancer at some stage of their lives. Epidemiological evidence has long pointed to a link between pregnancy in early life and a lower risk of breast cancer - although the reason why was not clear.
Experiments in animals show that pregnancy hormones influence a gene called P53 that produces a tumour suppressor protein. The same is thought to happen in people. In young women, whose breast tissue is still developing, this appears to have life-long effects. The effect is most marked in women who give birth before they are 20, said Professor O'Malley. The research is published in the journal Proceedings of the National Academy of Sciences.