SORBET trial

The SORBET trial examines whether women with triple negative metastatic breast cancer may benefit from taking the drug Tamoxifen to control the growth and spread of cancer cells.

About 15 per cent of all breast cancers are defined as triple negative, which means the cancer is not driven by either of the hormones oestrogen or progesterone, nor by the HER2 protein.

Triple negative breast cancer is often more aggressive than other types of breast cancer and women may have a poorer prognosis because the disease is more likely to spread to other parts of the body.

Those with triple negative breast cancer are usually treated with chemotherapy, however the SORBET clinical trial will look at whether Tamoxifen may be useful in controlling the growth of cancer cells in certain types of triple negative breast cancer.

The trial is run by the Australia New Zealand Breast Cancer Clinical Trials Group and will involve women from Australia and New Zealand.

Tamoxifen is not currently used to treat triple negative breast cancer, but has been used for many years to successfully treat women with oestrogen receptor positive (ER+) breast cancer. 

Studies have shown that the oestrogen receptor exists in two forms:
•    Oestrogen receptor alpha (ERα) which is traditionally used to determine the oestrogen receptor status of breast cancer; and
•    the lesser known Oestrogen receptor beta (ERβ). 

Some women with triple negative breast cancer may express oestrogen receptor beta, but not oestrogen receptor alpha.

Past research has shown that women diagnosed with potentially curable breast cancers which expressed the beta oestrogen receptor, but not the alpha, had longer survival times following treatment with Tamoxifen, when compared with women whose tumours did not express either oestrogen receptor.

The SORBET trial will test whether this is the case for women with triple negative breast cancer, which tests positive for oestrogen receptor beta, but not for oestrogen receptor alpha.  Around 20 per cent of women with traditional triple negative breast cancer are believed to be oestrogen receptor beta positive.

It is hoped that the SORBET trial will show that daily treatment with tamoxifen, a low cost and well tolerated drug, can control the growth and spread of triple-negative, ERβ-positive metastatic breast cancer.

If this is so, tamoxifen may add to the treatment options, which currently focus on chemotherapy, for these women. It may also lead to the investigation of tamoxifen as a treatment for triple-negative, ERβ-positive early breast cancer.

Results of this research will have implications worldwide in the treatment and management of women with this type of breast cancer.

SORBET will involve over 66 participants, including women in Auckland and Christchurch.  This trial is now closed and is in follow-up. For more information, please visit the Australia & New Zealand Breast Cancer Trials Group.