Causes of breast cancer
|AGE Risk increases with age||GENDER|
|LIFESTYLE Obesity, smoking, and delaying or avoiding pregnancy are risk factors||GENETICS In some cases, due to an abnormal gene|
The underlying cause of most breast cancers is unclear. However, it is thought that the female hormone oestrogen is an important factor in the development of the disease.
Women who have their first period before the age of 11 or who have a late menopause seem to be at increased risk of developing breast cancer, probably because their breasts are exposed to oestrogen for longer. Similarly, the number of menstrual cycles before a first pregnancy has some influence on the risk of breast cancer; for example, a woman who never has children is about twice as likely to develop breast cancer as a woman who has her first child before the age of 20. Breast-feeding is thought to have an additional protective effect.
Obesity slightly increases the risk of breast cancer because excess body fat causes an increase in oestrogen levels.
Artificial oestrogen in some medications may also influence susceptibility to breast cancer. Many cancerous tumours are oestrogen-sensitive, and oestrogen encourages them to grow once they have formed. Combined oral contraceptive pills slightly increase the risk of developing breast cancer, although only while they are being taken. Hormone replacement therapy in postmenopausal women is associated with a significant increase in risk, especially after 10 years of treatment.
About 1 in 20 cases of breast cancer is linked to an abnormal gene, and several of these genes have now been identified. Breast cancer with a genetic basis most commonly affects women in their 30s and 40s and may also affect men. If you have a close relative who had breast cancer before the age of 40, you may carry an abnormal gene and may be referred for genetic testing. The risk of developing breast cancer increases the more members of your family have had breast or ovarian cancer before age 40 (if close relatives have had breast cancer after age 40, the risk is only slightly increased). However, often, there is no family history of the disease. Noncancerous breast lumps do not increase the risk of breast cancer.
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