Whether a woman with breast cancer expresses a protein called HER-2 could help determine her course of chemotherapy — and whether or not she needs treatment with additional anti-tumour drugs, finds a new study.

The study suggests that women whose breast cancer expresses a protein called HER-2 are most likely to benefit from adding the drug Taxol to their chemotherapy regimen. Taxol (paclitaxel), made by Bristol-Myers Squibb, is a medication that inhibits tumour growth.

On the other hand, women whose tumours are fuelled by estrogen but do not express HER-2 may not benefit from adding Taxol to their treatment.

About 15 per cent to 20 per cent of breast cancers express HER-2, and as many as three-quarters of breast cancers are so-called estrogen-receptor-positive, according to the study.

The findings are published in the Oct. 11 issue of the New England Journal of Medicine.

"In general, chemotherapy for breast cancer has been a one-size-fits-all approach," says lead study author Daniel Hayes, clinical director of the breast oncology program at the University of Michigan Comprehensive Cancer Center, in a release. "With this data we hope we will be able to focus chemotherapy on patients whom it's most likely to help."

The study involved 1,500 women with node-positive breast cancer who were randomly assigned to receive two chemotherapy drugs, doxorubicin and cyclophosphamide. Half the study participants received an additional four cycles of Taxol. 

'We are not recommending at this time that women with positive lymph nodes, for whom we would currently recommend Taxol, but who are estrogen receptor positive and HER-2 negative not take the Taxol.' — Daniel Hayes, study author

Researchers found that the addition of Taxol improved survival rates in women who were HER-2-positive, regardless of their estrogen receptor status.

But women whose tumours were HER-2-negative and estrogen-receptor-positive had no additional benefit from Taxol.

The researchers say that because more study is needed, women with HER-2 negative tumours should consult their oncologists and not discontinue taking Taxol.

"We are not recommending at this time that women with positive lymph nodes, for whom we would currently recommend Taxol, but who are estrogen receptor positive and HER-2 negative not take the Taxol. We think the stakes are too high," said Hayes.

"We now believe, if these results are confirmed and validated in other studies, that perhaps we could pull out half the patients in that study and save them from the toxicities and the cost of receiving a drug that might not do them any good," he said.

Three of the authors of the study report receiving consulting fees from Bristol-Myers Squibb.