BREAST CANCERBreast cancer does not occur in children and the first cases are seen in the late teens and in the early twenties. At that age, the disease is rare but its frequency increases rapidly up to age fifty and then continues to increase, but less rapidly, thereafter. As we noted in the chapter on diet, there is a great deal of variation in breast cancer risk between countries. Social class is also a factor and the breast cancer rate at any age is usually considerably greater in higher socio-economic classes than in lower socio-economic classes. Whether this difference relates to diet or to other factors is still not clear.The breast is highly sensitive to hormones, particularly oestrogens. Breasts develop with the hormonal changes in puberty in girls. The cyclical changes in hormonen in the menstrual cycle affect breast tissues and their effect can sometimes be the cause of considerable discomfort. Hormones in pregnancy cause the breasts to increase in size and after delivery it is hormones that cause milk production. The most direct link between breast cancer and female hormones is very obvious —breast cancer is very rare in men.An important relationship between hormones and breast cancer is that the careful use of hormones can be a valuable aid to the treatment of breast cancer. Such therapy used to be carried out with the naturally occurring female hormones, oestrogens and progesterones, and these are still used. However, the best available drug at-present is not a naturally occurring hormone but a synthetic drug called Tamoxifen. This is remarkably well tolerated and is a very useful treatment for established cancers. Although we do not know exactly how Tamoxifen works, we know that it partly blocks naturally occurring hormones which can stimulate the growth of breast cancer.The features of the reproductive and hormonal cycles in women which are associated with an increased risk of breast cancer are:• An early onset of menstruation. Women whose periods begin at the age of twelve or before and who rapidly establish regular cycles are several times more likely to develop breast cancer than those whose menstruation does not start until after the age of thirteen.• A late menopause. Women whose menopause occurs before the age of forty-five have only about half the risk of breast cancer of those whose menopause occurs after the age of fifty-five.• No pregnancies, or late pregnancies. Women who have lots of babies are less likely to get breast cancer than women who do not This explains why breast cancer is, commoner in single women and in married women who have no children. Most of this effect is determined by the age of the mother when the first baby is born. Women who have their first baby under the age of twenty have only about half the risk of breast cancer of a woman who never has a child. If the first child is born at around about thirty to thirty-five years then there is virtually no protective effect and the risk of getting breast cancer is about the same as that of a woman who has never had a child. If the first child is born when the mother is more than thirty-five years old then the risk of getting breast cancer is probably slightly greater than that of the childless women.No one can extend these observations into a recommendation that women should all have their children early. There are many other factors that operate in these decisions. Nevertheless, the observations seem to be real and cannot be ignored. They lead us to reinforce the advice that women aged fifty to sixty-four should have careful breast cancer screening. Such advice would be particularly true for those whose age at first motherhood was more than thirty.*87\194\4*

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