Many patients are given the powerful drugs to destroy any cancer cells that may have spread.

But according to research, published in the Journal of the National Cancer Institute, the treatment does not increase the survival rates for some women.

The finding adds to the growing debate about the use of chemotherapy to treat some breast cancer sufferers.

The latest findings apply to postmenopausal women suffering from a type of breast cancer that is sensitive to the hormone oestrogen.

'Unnecessary discomfort'

Chemotherapy after surgery did not increase their survival odds, according to a trial of 1,669 patients from many countries.

But it was of "decided benefit" to patients whose tumours were unresponsive to oestrogen, say the study's co-authors, from the Dana-Farber Cancer Institute in New England.

Dr Richard Gelber, who headed the statistical analysis, says cancer treatments need to be more finely "tailored" to patients to avoid unnecessary discomfort and expense.

He hopes the work will cause physicians to examine more carefully whether post-menopausal women with oestrogen-sensitive tumours that have not spread should routinely be offered chemotherapy.

These women have a better prognosis because they can be given the drug tamoxifen, which blocks the action of oestrogen and stops tumours growing.

Quality of life

According to the charity Breast Cancer Care, chemotherapy is increasingly given in addition to surgery and radiotherapy in the UK.

Significant numbers of women may be able to avoid the side effects associated with chemotherapy but still have the same prospects for survival

Kate Law, Cancer Research UK

In most cases chemotherapy is given after surgery, and before radiotherapy, although this can vary.

US doctors have a greater tendency than European ones to offer chemotherapy, which can have unpleasant side effects.

The study found that patients who underwent chemotherapy felt more poorly and in some cases lost their hair.

"This means that they felt different during chemotherapy and it should not be used frivolously," says Dr Gelber.

"But on the other hand, this transient reduction in the quality of life should not be used as an excuse to deny chemotherapy when it can be helpful."

Kate Law, head of clinical trials at the medical research charity Cancer Research UK, said it was an extremely important trial.

She said the results "potentially mean that we can identify much more clearly which women with breast cancer will benefit from chemotherapy and those that will not".

"This means that significant numbers of women may be able to avoid the side effects associated with chemotherapy but still have the same prospects for survival," she told BBC News Online.