The density of tissues within the breast is a key determinant of breast cancer, a new study has shown.
A paper published in today's Journal of the National Cancer Institute reports that breasts with less fatty tissue and more tissues like milk glands are more likely to develop cancer.
Tumours in dense breasts are harder to detect during mammogram scans but researchers at the Group Health Centre for Health Studies in Seattle believe that women with dense breasts are also more likely to develop tumours.
"Although breast cancer is harder to detect in women with dense breasts, our research showed that women with dense breasts are more likely to develop breast cancer," confirmed Dr William Barlow, the article's lead author and researcher with Group Health.
As a result, breast density now joins a number of other well-known factors which increase the risk of breast cancer, including age and family history.
Breast cancer is the most common cancer in women, affecting around one million women worldwide.
Each year, over 41,700 women and 300 men are diagnosed with breast cancer in the UK, resulting in more than 12,400 deaths annually, according to Cancer Research UK.