Hormones

Most breast cancer is sensitive to the female hormone oestrogen. Sensitive cancer cells need oestrogen to stay alive and removal of oestrogen from the body or stopping any circulating oestrogen getting to the cancer cells is very effective at controlling or killing hormone-sensitive breast cancers. It is possible to determine whether a tumour is sensitive to hormones by performing a chemical test on the tumour. Tumours can be classified into oestrogen sensitive and oestrogen insensitive tumours. In premenopausal women who are still having regular menstrual periods, about half of all breast cancers are hormone sensitive. Over two thirds of tumours in postmenopausal women whose periods have stopped are oestrogen sensitive. The most commonly used medicine against oestrogen sensitive tumours is tamoxifen (eg Nolvadex D). This medicine is an anti-oestrogen in its effect on breast cancers and works by stopping oestrogen getting to the cancer cells. It appears to be a very safe medicine but can cause side effects which can be distressing and these include flushing (similar to those women experience during the menopause), vaginal dryness and vaginal discharge. Many women complain of weight gain on tamoxifen, but, in randomised studies, women taking tamoxifen put on a similar amount of weight to those women who were not receiving drug treatment. There is an increased incidence of eye problems and disturbance of vision. This is reversible if the medicine is stopped. The most serious possible side effects of tamoxifen are that it can slightly increase the incidence of cancer of the lining of the womb, and slightly increase the risk of a blood clot in the leg (deep vein thrombosis). However the risks of both these side effects are very low. Tamoxifen has been widely used throughout the world and is a very safe medicine for pre and postmenopausal women. Few women have to stop the medicine because of side effects. Women who have had surgery for early breast cancer are commonly given tamoxifen following the surgery to reduce the risk of recurrence of the cancer. The production of oestrogen in postmenopausal women requires an enzyme called aromatase. A new class of medicines for treating breast cancers blocks this aromatase enzyme. These medicines are called aromatase inhibitors and include letrozole (Femara), anastrazole (Arimidex) and exemestane (Aromasin). They are very effective in postmenopausal women with oestrogen sensitive tunours. The side effects include flushings, nausea and lack of appetite. Occasionally, women have to stop the medicine because of the constant feeling of sickness. In premenopausal women the major source of oestrogen is the ovaries. Either removing the ovaries or using an injectable medicine called goserelin (Zoladex), which stops the ovaries from producing oestrogen are effective treatments in hormone sensitive breast cancer. The medicine which stops the ovaries working has to be injected once a month. Side effects of this type of medicine or removal of the ovaries include the rapid onset of menopausal symptoms.