Breast cancer and oestrogen

Breast cancer affects one in 12 Australian women, with around 2,600 Victorians diagnosed as having the disease every year. There are different types of breast cancer. Around 60 per cent are sensitive to the female sex hormone oestrogen. These cancers are called receptor positive cancers. Paradoxically, breast cancer is more common in postmenopausal women, whose oestrogen levels have dropped to the point where ovulation is no longer possible. It seems that oestrogen is also made inside breast tissue. Medications such as tamoxifen can block the action of oestrogen and prevent it from stimulating the breast cancer cells.

Breast cancer and women of childbearing age
Menstruating women who have hormone responsive breast cancer can benefit from hormone therapy. Interest in oestrogen and its link to breast cancer was first sparked when it was noticed that a side effect of chemotherapy - stalled menstrual cycle - happened to improve a woman’s chances of recovery. Research is now looking at the effects of blocking oestrogen in young women to starve their breast cancers. For example, luteinising hormone releasing hormone (LHRH) can be used to plummet oestrogen to postmenopausal levels. The menstrual cycle recovers after the end of treatment. Hormone therapy may be combined with chemotherapy. Each person should make a decision about whether or not to have chemotherapy in consultation with their doctor. The decision should be made after all available information on the benefits and risks has been fully discussed.

Oestrogen in the postmenopausal woman
Breast tissue contains fat cells. These cells make an enzyme called aromatase, that produces oestrogen. In normal breast tissue, the amount of aromatase is carefully regulated. As a woman ages, the fat cells of her breasts tend to produce greater and greater amounts of aromatase, which in turn increases the amount of local oestrogen. This seems to play a role in triggering breast cancer in postmenopausal women. Once established, the tumour further increases oestrogen levels, which helps it to grow. Immune cells that flock to the tumour also seem to boost oestrogen production.

Hormone therapy
After surgery to remove the hormone responsive tumour, drugs such as tamoxifen can be used to block the action of oestrogen and lower the risk of recurrence. Current research is focusing on newer compounds designed to block oestrogen production in the breast only, as oestrogen is still needed for - amongst other things - healthy bones. Possible side effects of tamoxifen include:

• Hot flushes
• Reduced appetite
• Stomach upsets
• Dizzy spells
• Leg cramps
• Respiratory problems
• Increased risk of blood clots
• Slight increased risk of cancer of the lining of the uterus.

• Your doctor
• Cancer Council Victoria Information and Support Service Tel. 131 120

• Around 60 per cent of breast cancers are sensitive to the female sex hormone oestrogen.
• The growth of cancer can be minimised by taking drugs that block the action of oestrogen in the breasts.
• Side effects of hormone therapy include dizzy spells, hot flushes and respiratory problems.

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