Research at the Cancer Epidemiology Unit aims to identify causes of human cancer that are potentially modifiable. Emphasis is on common cancers and on external causes of cancer, such as diet and exposure to hormones, infectious agents and radiation. Emphasis is also on quantifying risk, because for some exposures, such as hormones and ionizing radiation, the issue is not so much whether they cause cancer but rather which patterns of exposure are most hazardous and the magnitude of the effects.
Breast cancer is the most common cancer in women worldwide.
Several research projects aim to describe and quantify the way in which hormonal, reproductive and other factors affect breast cancer risk. The Collaborative Group on Hormonal Factors in Breast Cancer was established in 1992, with its secretariat based in Oxford. About 200 researchers from 30 countries have contributed relevant data on almost 200,000 women to the collaboration, which aims to investigate the role of hormonal, reproductive, and other factors on breast cancer. The first two reports of the group, on the relationship between breast cancer and use of oral contraceptives and of use of hormone replacement therapy, showed that there was a small increase in the risk of breast cancer while women were using either type of hormonal therapy and in the few years after stopping. There was, however, no evidence of any residual increase in risk of breast cancer many years after ceasing use of either type of therapy.