CANCER AND BREAST CHANGES THROUGHOUT LIFE
Clearly, the breast is an organ that changes throughout life in response to changes in hormone levels (arising from puberty, pregnancy, breastfeeding, menopause, or drug therapies such as oral contraception and hormone replacement therapy). It follows from the above observations that medical treatments that affect hormone levels may alter the risk of developing breast cancer. Hormone replacement therapy (HRT) is widely used for menopausal symptoms. It was hoped that, in addition to helping ameliorate symptoms such as hot flushes and loss of libido, HRT would prevent diseases that tend to occur with increasing frequency after the menopause such as heart disease and bone loss (osteoporosis) with a consequent risk of fracture. While HRT is indeed effective in some of these aims, it also appears to increase the risk of breast cancer with prolonged use. A similar effect is seen with the oral contraceptive pill, which again works by altering the normal hormone environment. These, then, are confusing effects: some hormone changes (those associated with pregnancy and breastfeeding) protect against breast cancer, while other changes (oral contraception and HRT) increase risk. Against this background, much laboratory research is focused on the role that hormones play in the causation of breast cancer and on the development of drugs that interfere with hormone pathways and thereby treat breast cancer. One of these drugs, tamoxifen, which acts mainly by blocking the effects of the hormone oestrogen, can be regarded as one of the most effective drugs of all time, having saved the lives of probably millions of women and helped prolong life for many more in the 25 or so years since it came into clinical use.
Finally, there is a perception, promoted to a degree by groups campaigning for better treatment and research, that breast cancer is a disease of young women. In general, as we have already seen, this is inaccurate. However, studies of patterns of risk of breast cancer revealed that some families appear to be at very high risk of breast cancer, with mothers, sisters, aunts all affected at an early age, often with disease in both breasts or associated with cancer of the ovaries, or of the prostate in the male relatives. These families were obvious candidates for in-depth study and, given the very obvious risks to the families involved, sufferers were often very receptive to participation in research. Studies of the patterns of inheritance in such cases suggested that the risk of breast cancer was passed on from mother to child with a 50:50 risk, and suggested at least two common inherited forms of the disease plus a number of less common versions.