A trial looking at blocking oestrogen from the ovaries in premenopausal women with hormone receptor positive early breast cancer (SOFT)

This trial was done to find the best way of stopping breast cancer from coming back in premenopausal women. The trial was supported by Cancer Research UK.

Some breast cancers are oestrogen receptor positive (or ER positive). This means they grow in response to the hormone oestrogen. In women who haven’t been through the menopause, oestrogen is made in the ovaries. After the menopause, the ovaries no longer make oestrogen, but a small amount is produced in fat tissues and by the adrenal glands.

Doctors usually treat premenopausal women who have ER positive breast cancer with the hormone therapy drug tamoxifen, alongside other treatments such as surgery, radiotherapy or chemotherapy. Tamoxifen blocks receptors on breast cancer cells and helps to stop the cancer coming back after surgery.

Another group of drugs used to treat ER positive breast cancers are aromatase inhibitors. These drugs work by reducing the amount of oestrogen the body makes. They don’t block oestrogen made by the ovaries. But they block the small amounts made in fat tissues and the adrenal glands in women who have been through the menopause.

In this trial, the researchers wanted to see how well the aromatase inhibitor, exemestane worked for women who had not been through the menopause.

As their ovaries were still working, the women also had treatment to either remove or ‘switch off’ their ovaries and stop them making oestrogen. Switching off the ovaries is called ovarian function suppression or OFS.

Doctors sometimes recommend OFS to premenopausal women who are taking tamoxifen. But they are not sure how much extra benefit women get from this, particularly if they also have chemotherapy after surgery.

The women taking part in this trial had one of the following treatments

• Tamoxifen for 5 years

• Tamoxifen for 5 years, plus treatment to switch off the ovaries (ovarian function suppression or OFS)

• Exemestane for 5 years plus OFS

The aim of the trial was to find out which treatment was better at stopping breast cancer from coming back in premenopausal women.