Hormone receptor positive (HR+) breast cancer is the most common type in New Zealand, accounting for about 75% of cases. The cancer cells in tumours of this type have an abundance of receptors for the hormones oestrogen (ER+) and/or progesterone (PR+), meaning that their proliferation is driven by these hormones.
Depending on the stage and grade of the cancer, HR+ breast cancer treatment usually begins with surgery, radiotherapy and chemotherapy, followed by hormone therapy to block the effects of oestrogen and/or progesterone on any remaining cancer cells. The goal of hormone therapy is to prevent the breast cancer from spreading or returning.
Nearly half of the cases of HR+ breast cancer recurrence happen more than five years after the initial diagnosis [1], so hormone therapy needs to be taken for several years to be most effective.
Tamoxifen and aromatase inhibitors, such as anastrozole, letrozole or exemestane, are medicines commonly prescribed as hormone therapy. Both come in pill form.
Tamoxifen, which blocks oestrogen’s effects on cancer cells is used in both pre- and post-menopausal women.
Aromatase inhibitors, which reduce oestrogen production in the body, are mostly prescribed to post-menopausal women. After menopause, our ovaries no longer produce oestrogen, but some is produced elsewhere in our bodies, mainly in fatty tissue. Aromatase inhibitors can shut down oestrogen production in these tissues, so that there is less in our bodies to stimulate a breast cancer recurrence.
Ovarian suppression is another way to reduce oestrogen levels in pre-menopausal women. Goserelin is an injection which temporarily stops the ovaries producing oestrogen. Oophorectomy (surgical removal of ovaries) is another option for some women, permanently stopping ovarian oestrogen production.
Hormone therapy needs to be taken for between five and ten years to be effective. Over that time, it is not unusual for there to be dose adjustments and/or changes in the medicines used. Other medicines might also be needed to manage side effects. Because oestrogen performs many different functions in our bodies, therapies that lower oestrogen levels can produce noticeable side effects. Hormone therapy is a ‘long game’ with proven benefits for preventing recurrence and improving survival [2].
You can read more about hormone (endocrine) therapy, its side effects and managing them, by clicking here.
References:
[1] Thomas et al. Late recurrence following early breast cancer. Journal of Clinical Oncology. 2022 Mar 3;40(13):1400-1406.
[2] Symonds and Davidson. Are we there yet? Optimal duration of endocrine therapy in women with postmenopausal early-stage hormone receptor-positive breast cancer. JNCI 2023, 115(11), 1240-1242.
20 September 2025
