Prevalence and risk factors
Breast cancer is the most commonly diagnosed cancer in women in both the UK and the US (Cancer Research UK, 2005; American Cancer Society, 2005). In the UK, around 41 000 women develop breast cancer and around 13 000 die from the illness each year. In the US, approximately 210 000 women are diagnosed and 40 000 die from breast cancer every year. It is possible for men to develop breast cancer but it is rare, with annually fewer than 300 cases in the UK and 1700 in the US.
International comparisons (Parkin & Muir, 1992) and studies of migrants (Kolonel, 1980) have provided evidence for the importance of environment in causing the disease. These observations are significant because they suggest that some breast cancers are caused by lifestyle and therefore could be prevented. The major risk factors for breast cancer include (see Colditz et al., 2000): older age, being overweight after the menopause, having a family history of breast cancer, taking the oral contraceptive pill or hormone replacement therapy, starting menstruation early or having a late menopause, starting to have children at an older age, having fewer children, not breastfeeding and regularly drinking large amounts of alcohol. Fewer than 5% of breast cancers arise from inherited gene mutations such as BRCA1 and BRCA2 (Hodgson & Maher, 1999).
Early detection
Screening
Screening mammography has been found to reduce breast cancer mortality in women aged between 50–74 years (Kerlikowske et al., 1995), while the benefits of screening women aged 40–49 years are not so clear (Moss, 2004).