Hope on resistant breast tumours

More trials are needed

An anti-oestrogen compound has been found to combat the growth of breast cancer in tumours that are resistant to the most widely used anti-oestrogen drug, tamoxifen.

The compound, known as TAS-108, is being assessed in preliminary clinical trials in the USA, the European Breast Cancer Conference in Barcelona, was told.

We believe we have a new tool for combating oestrogen-dependent breast cancers

Yasuji Yamamoto

The drug not only inhibits the growth of oestrogen-dependent breast tumours, but appears to exert a protective effect on the skeleton and the cardiovascular system and may not cause the side effects associated with tamoxifen, scientists suggest.

Significant

Dr Tetsuji Asao, product director of Taiho Pharmaceutical Co. Ltd. - the company that developed TAS-108 - said this was a significant discovery.

He said: "We believe TAS-108 is a promising anti-oestrogen for the treatment of breast cancer patients.

"In particular, it appears to inhibit the growth of tamoxifen-resistant tumours."

The team now plans to confirm its efficacy in breast cancer patients who have become resistant to tamoxifen in follow-up trials.

Dr Asao said: "Obviously we need to continue to test its efficacy and safety in phase II and III clinical trials, but if these prove successful, we believe we have a new tool for combating oestrogen-dependent breast cancers which have proved to be resistant to other anti-oestrogen drugs."

Since its discovery, Yasuji Yamamoto and colleagues at the University of Tokyo in Japan, have been trying to find out how the compound works.

Comparisons

They compared TAS-108 with other leading anti-oestrogens - tamoxifen, raloxifene and faslodex.

They found only faslodex matched TAS-108 in its ability to inhibit the activities of the oestrogen receptors on the tumour cells, while tamoxifen and raloxifene were only partially successful.

However, TAS-108 differed from faslodex in one crucial area, which made it far more effective than any of the other anti-oestrogens - it recruited the help of a substance to help it block the activities of the oestrogen receptors.

This same substance was activated by tamoxifen and raloxifene, (but not by faslodex) but it swung into action far more vigorously with TAS-108.

Mr Yamamoto said: "Based on these findings, we conclude that TAS-108 could be classified as a unique anti-oestrogen, successfully inhibiting the growth of oestrogen-dependent breast tumours, including tamoxifen-resistant tumours."

Tests have also found that unlike tamoxifen, TAS-108 inhibited breast tumours in rats without any effect on the uterus.

One of the side effects of tamoxifen can be a slightly increased risk of endometrial cancer.