Drug halves breast cancer returns

But the treatment only works in women whose breast tumours carry excessive amounts of a protein known as HER2 that makes the cancer particularly aggressive, and on occasion may cause serious side effects.

About one in five women with breast cancer have such tumours.

The drug is trastuzumab, sold under the brand name Herceptin by Genentech in the United States and by Swiss drugmaker Roche in Europe.

Approved in 1998 to treat breast tumours that have spread, routine use of the drug cuts the recurrence rate by nearly 50 percent, at least over the short term, two new studies in The New England Journal of Medicine show.

"This is a very important finding. It's likely to change the recommended care for patients. But we need to know more about the side effects and the long-term effectiveness," said Richard Gelber of the Dana-Farber Cancer Institute and an author of one study known as the HERA study.

"The results are simply stunning," said Gabriel Hortobagyi of the University of Texas MD Anderson Cancer Center in Houston, who predicted in a Journal editorial that the findings "will completely alter our approach to the treatment of breast cancer."

SIDE EFFECTS

But there are potentially troubling side effects.

Trastuzumab can damage the heart in some women, although the problems usually fade if the drug is discontinued, Gelber told Reuters. In addition, women who receive the drug after breast cancer surgery are more likely to develop subsequent tumours in the brain or elsewhere in the nervous system.

But in an era when doctors are happy if a drug improves the survival rate by just a few percentage points, a medicine that cuts the tumour recurrence rate by nearly 50 percent is considered a significant improvement.

Only tamoxifen, a mainstay of cancer treatment, produces such good results, said Hortobagyi. HER2 tumours tend to be resistant to tamoxifen, said Harold Burstein of Dana-Farber.

Researchers must still determine if trastuzumab would work even better if given in chemotherapy or for more than a year.

In the HERA study, sponsored by Roche, 3,387 women in 39 countries were given standard surgery and chemotherapy but half received trastuzumab every three weeks for a year.

A year after treatment ended, doctors found only 127 instances of death, new cases of breast cancer or some other type of tumour among the trastuzumab recipients compared to 220 such cases among volunteers who did not get the drug.

About six percent of the patients stopped taking the drug because of adverse results. The risk of heart problems was low, the study said, "but this could change with longer follow-up."

Results of the second study, actually a combination of two studies partly funded by Genentech, were released in April by the US National Institutes of Health. They found a similar reduction in death or new cancer among women who got trastuzumab while receiving conventional chemotherapy.

But the rate of heart problems was much higher -- 4.1 percent against less than 1 percent in the HERA study.