When deciding about hormonal therapies it’s important to consider the likely benefits and possible side effects of the different treatments.

Hormonal therapies and early breast cancer

For women with early breast cancer, the long-term benefits and risks of taking tamoxifen are well known. Tamoxifen reduces the risk of breast cancer coming back and improves survival.

Studies have shown that treatment with an aromatase inhibitor reduces the risk of breast cancer coming back more than tamoxifen. However, studies have not been going long enough to say whether aromatase inhibitors improve survival more than tamoxifen. Also, we do not yet know the long-term side effects of aromatase inhibitors.

For post-menopausal women with a higher risk of breast cancer coming back, the short-term benefits of aromatase inhibitors outweigh the risks of side effects (both known and unknown).

For post-menopausal women with a lower risk of breast cancer coming back, it’s possible that long-term side effects of aromatase inhibitors (as yet unknown) outweigh the short-term benefits of treatment compared with tamoxifen.

CYP2D6 test for the effectiveness of tamoxifen

A number of consumers have raised questions about the effectiveness of CYP2D6 genotype testing for women considering tamoxifen as treatment for breast cancer.   

There have been a number of studies looking into the potential role of CYP2D6 genotype testing (a blood test) as a marker for whether an individual will be resistant to treatment with tamoxifen.

Currently, there is not enough evidence to recommend routine testing for the CYP2D6 genotype when making clinical decisions regarding the use of tamoxifen in either pre or post menopausal women.

Cancer Australia recommends consideration of the use of adjuvant hormonal therapy for most women with hormone receptor-positive early breast cancer. Women should make decisions about which hormonal therapy is most suitable for them in consultation with their medical oncologist.

As the biology of breast cancer is becoming better understood, the management of breast cancer is increasingly being tailored according to patient and tumour factors. Cancer Australia will continue to monitor new evidence and provide updated information as appropriate.

Hormonal therapies and metastatic breast cancer

For women who haven’t yet reached menopause and who have hormone receptor-positive breast cancer, treatment usually starts with tamoxifen with or without an ovarian suppression drug.

For women who have reached menopause and who have hormone receptor-positive breast cancer, treatment usually starts with an aromatase inhibitor. If a woman is already taking tamoxifen when her metastatic  breast cancer is diagnosed, it’s recommended that she changes to an aromatase inhibitor.

If a woman’s metastatic breast cancer stops responding to treatment with an aromatase inhibitor, or if she has side effects that are difficult to manage, she may be advised to change to a different type of hormonal therapy.

In general, fulvestrant and progestins are only recommended if other hormonal therapies have stopped controlling the cancer.