BREAST CANCER: HORMONES AND SMOKING AS RISK FACTORS
The role of female hormones
The fact that breast cancer is about 100 times more common in women than in men suggests a role for the female sex hormones.
Women whose first period occurred at a young age seem to be more at risk of developing breast cancer, as are those who have had their first child late (at 30 to 34 years old), and those who have had a late menopause. It seems that the longer a woman is exposed to her own female hormones – particularly oestrogen -the more at risk she is. Some diets which can lead to obesity, particularly those high in fats, can also lead to an earlier onset of menstruation. Thus girls in the well-nourished and high socioeconomic groups of the industrialized West, where the incidence of breast cancer is high, tend to have their first periods younger than those in areas of malnutrition where the disease is less common.
In pre-menopausal women, it is the ovarian oestrogen which is relevant, and this is produced for as long as menstruation continues. Breast cancer is less common in women who have had an operation to remove their ovaries in their 30s or 40s, before their menopause.
In the past, the doses of oestrogen used in hormone replacement therapy (HRT) may have been linked to a slightly increased risk if taken for longer than 10 years. HRT is now normally given as a combination of oestrogen and progestogen, and the drug doses are much lower. There is no evidence that modern HRT is linked with the development of cancer; in fact, some doctors continue to give it to women who have breast cancer.
Modern contraceptive pills – which also contain a very low hormone dose – have little apparent risk. They do, however, reduce the risk for endometrial and ovarian cancers. Fibroadenomas in the breast are also less common in women taking the low-dose contraceptive pill.
Smoking
Cancer cells may spontaneously develop at any time and are usually destroyed by the body’s immune system. As smoking suppresses the immune system, it is not surprising that all cancers are more common in those who smoke.
Other risk factors
Other risk factors have been suggested, but with less supporting evidence. For example, there may be a small, but real, link between high alcohol consumption and breast cancer. Stress, either the experience of it or the way it is dealt with, has also been implicated.
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