About 2 out of every 3 breast cancers rely on a supply of the female hormone oestrogen to stimulate their growth. These tumours are known as oestrogen receptor positive (ER+) cancers.

In women who are pre-menopausal (having monthly periods) the main source of oestrogen is the ovaries. After the menopause, women make smaller amounts of oestrogen from other tissues in their body.

Anastrozole is a type of drug called an aromatase inhibitor. Aromatase inhibitors stop oestrogen being produced after the menopause. They don’t stop the ovaries from making oestrogen. So they are usually only used to treat women who have passed the menopause.

Goserelin (Zoladex) stops the ovaries from producing oestrogen. It is used to treat women who are still menstruating.

Tamoxifen works in a different way to both the aromatase inhibitors and Zoladex. It can be used to treat both pre- and post-menopausal women.

A small number of research studies have shown that combining Zoladex and an aromatase inhibitor can be an effective treatment for pre-menopausal women who have ER+ tumours and whose breast cancer has come back after treatment with tamoxifen.

Clinical trials are going on to find out whether combining a treatment that stops the ovaries producing oestrogen (such as Zoladex) with an aromatase inhibitor is as effective as tamoxifen in pre-menopausal women with ER + breast cancer. In the UK a study called the SOFT trial is looking at this. There is more information in the trials section of our website.

Until the results of these trials are available we won’t know if taking an aromatase inhibitor, such as anastrozole, with Zoladex, is as good a treatment as tamoxifen for younger women with breast cancer.

References

• Jonat W et al. Trends in endocrine therapy and chemotherapy for early breast cancer: a focus on the premenopausal patient. J Cancer Research and Clinical Oncology, 2006; 132: 275-286
• Celio L et al. Premenopausal breast cancer patients treated with a gonadotropin-releasing hormone analog alone or in combination with an aromatase inhibitor: A comparative endocrine study. Anticancer Res 1999;19:2261-8. Abstract
• Cheung KL et al. The combined use of goserelin and anastrozole as second line endocrine therapy in premenopausal women with advanced breast cancer - a study of its clinical and endocrine effects. Proc ASCO 2001; Abstract 1937.
• Forward D et al. Combined use of goserelin (Zoladex) and anastrozole (Arimidex) in premenopausal women with metastatic breast cancer (MBC). Proc ASCO 2000; Abstract 582.