The causes and prevention of breast cancer

Valerie Beral

University of Oxford, UK

Breast cancer is the most common cancer in women worldwide, with over 1 million new cases occurring annually. Incidence rates used to be 6-7 times more common in developed than in developing countries, but the gap is narrowing, as breast cancer rates in developing countries are now increasing rapidly.

The relative contribution to the total burden of breast cancer from the well-established and potentially modifiable causes will be described. By far the most important reason why women in developed countries have such high rates of breast cancer is because, on average, they have comparatively few children and breastfeed for a relatively short time. However, it is neither feasible nor desirable for women to revert to childbearing patterns of the past to prevent breast cancer.

If we seriously want to prevent breast cancer on a scale that could really make a difference, we need to understand exactly how childbearing in early adult life provides lifelong protection against breast cancer. Surprisingly little is known, except that some of the hormones produced in late pregnancy and during lactation are involved. If we knew the precise mechanisms, it should be possible to achieve sizeable lifelong protection against breast cancer from relatively short-term exposures to the appropriate hormones during early adult life.