English studies

Removal of ovaries reduces risk of breast cancer

Ovariectomy, or removal of the ovaries, significantly reduces the risk of developing breast cancer among women who are genetically predisposed to cancer. This preventive effect has just been confirmed again by a huge international study that identified optimal conditions.

Women predisposed to breast cancer carry BRCA1 or BRCA2 gene mutations. In the general population, close to 5 per cent of women are affected, but the numbers double among French Canadians and Ashkenazi Jews. In fact, the risk for these groups of developing breast cancer is as high as 80 per cent at the age of 80. These women are also at risk of developing ovarian cancer, at a rate of 20 per cent for BRCA2 mutations, and 65 per cent for BRCA1 mutations.

Since these two forms of cancer are related in some ways, doctors have observed that ovariectomies among women with a mutation and with ovarian cancer reduce the risk of later developing breast cancer. This effect is attributed to a decrease in estrogen levels. However until now, due to insufficient data, it has not been possible to determine the impact of this procedure on breast cancer prevention.

A team of 20 researchers from as many research centres around the world, including epidemiologist Parviz Ghadirian of the Unité de recherche en épidémiologie du CHUM (Hôtel-Dieu), conducted one of the first major studies on the topic. They collected data on 3300 women with one of the two gene mutations; 43 per cent had been diagnosed with breast cancer, and the others constituted the control group.

The results, published in the October 24, 2005 issue of the Journal of Clinical Oncology, show that ovariectomy helped to reduce the risk of breast cancer by 46 per cent among women with BRCA2 mutations, and by 56 per cent among women with BRCA1 mutations. According to the researchers, this difference may be related to biological characteristics of the tumours caused specifically by one of the mutated genes, their proteins being slightly different. It is known, for instance, that the preventive effect of breastfeeding, oral contraceptives and tamoxifen of breast cancer is less significant in the case of BRCA2 mutations.

The study also showed that the preventive effect of ovariectomies continued to be observable for at least 15 years after the operation. This effect is even more significant if the operation is performed early: for carriers of the BRCA1 gene mutation, the risk reduction is up to 64 per cent if the operation is performed before the age of 40 and 50 per cent when the surgery takes place between the ages of 40 and 50. After the age of 50, ovariectomies do not have any significant statistical impact.

The authors of the study therefore recommend that women predisposed to breast cancer consider a preventive ovariectomy as of the age of 35. In Canada, 60 per cent of these women are already taking this advice. Removal of the ovaries can, however, cause the early onset of menopause.