Breast cancer is the most common form of malignancy in women. The cancer may be non-invasive at diagnosis - ductal carcinoma in situ - where it remains confined to the ducts. However in most patients it is invasive, it may have spread beyond the immediate site of origin at diagnosis. The aim of treatment is always to reduce mortality, increase progression-free and disease-free survival and improve the quality of life. The management of patients involves surgery, radiotherapy and drug therapy, or a combination of them.
Drug therapy (chemotherapy) aims to reduce the risk of recurrence, invasion and metastases. In advanced disease - where cure is not expected treatment aims to induce remission, prolong disease-free survival, to relieve symptoms and improve the quality of life. Chemothrapy can be given after surgery (adjuvent chemotherapy) or before surgery (neoadjuvent chemotherapy) with the goal of reducing tumour size (downsize the tumour) to make breast-conserving surgery possible.
Oestrogen is important for the treatment of breast cancer in a number of ways.
1. Breast cancers can grow under the influence of ovarian oestrogen
Normal breast cells, that are not cancerous, grown under can grow under the influence of oestrogen (estrogen). Breast cancer cells that maintain the oestrogen receptor (ER+ breast cancer*) continue to use oestrogen as a growth factor. In pre-menopausal women, continuing to make oestrogen from their ovaries it is important to block that oestrogen acting on breast cells, particularly breast cancer cells that might have not been removed at surgery and/or not damaged or destroyed by chemotherapy and/or radiotherapy, because the oestrogen may make those cells grow and proliferate causing recurrent disease. Tamoxifen is an oestrogen receptor blocker that is used in the management of breast cancer in pre-menopausal women.
2. Breast cancers can grow under the influence of locally produced oestrogen
Small amounts of oestrogen are produced all round the body by a process called aromatisation. If there is no ovarian oestrogen ER+ breast cancer can be effectively treated by aromatase inhibitors like anastrazole, letrozole and exemestane. These drugs cannot be used in pregnancy, breast feeding or if pregnancy might occur unless there is secure contraception as these drugs can damage the developing baby. Pre-menopausal patients who have had disease progression despite tamoxifen may be prescribed drugs (goserelin) to suppress their own ovaries to enable them to take aromatase inhibitors..
3. Breast cancer chemotherapy may cause temporary or permanent ovarian failure.
The matter is further complicated by the fact that adjuvant or neoadjuvant chemotherpy can damage the ovaries temporarily or permanently. The oncologist in this situation may need to consult with an endocrinologist, or a specialist gynaecologist, to determine what the state of the ovaries are, and in particular whether tamoxifen, aromatase inhibitor alone or an aromatase inhibitor with goserelin.
*There are other receptors that are important for breast cancer including the progesterone receptor and the HER-2 receptor.
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