msnbc.com news services
updated 12/9/2004 12:38:29 PM ET 2004-12-09T17:38:29

Arimidex, one of a new class of breast cancer drugs, has clearly beaten standard treatment tamoxifen at preventing breast cancer from returning in a 5-year study, researchers said on Wednesday.

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The drug, Arimidex, might be able to prevent 70 percent to 80 percent of the most common type of tumors that occur in women after menopause, compared to the 50 percent that tamoxifen is credited with warding off, the research suggests.

Women given Arimidex had an extra 10 percent of cancer-free life compared with those on tamoxifen and the newer drug increased the time to disease recurrence by around 20 percent.

In addition, the spread of cancer, called metastasis, was reduced by 14 percent and the risk of cancer occurring in the other breast was cut by more than 40 percent.

“Arimidex is a more effective treatment. This is a better drug,” said Dr. Aman Buzdar, a specialist at the University of Texas’ M.D. Anderson Cancer Center. He headed the U.S. portion of the study, which involved nearly 2,000 American women and an additional 7,300 from 20 other countries.

It was funded by Arimidex’s maker, AstraZeneca PLC. Results were reported Wednesday at a meeting in Texas of breast cancer experts and were published online by the British medical journal The Lancet.

Falls short on overall survival
Arimidex, which is also known by the generic name anastrozole, had already been shown to have significant benefits over tamoxifen in 3-year tests and the longer-term advantages are likely to increase demand for the newer drug type.

The newer drugs are associated with fewer side effects than tamoxifen — which has been in use for more than 20 years — although researchers said bone fractures and joint pain were more common in women on Arimidex.

Previously, many doctors were reluctant to recommend it instead of tried-and-true tamoxifen, which has long been available in cheap, generic form, on early results alone. Just last month, the world’s largest group of cancer specialists, the American Society for Clinical Oncology, published new guidelines saying aromatase inhibitors were promising drugs that at some point should be part of most breast cancer patients’ treatment, but did not spell out which drugs should be used for which women and when.

The new five-year results on Arimidex are the most definitive, finding that the drug improved disease-free survival by 26 percent over tamoxifen.

The latest facts and figuresYet they fall short of meeting the toughest standard for proving a drug’s value — improving overall survival. Doctors in and outside the study say that women in the study had very early cancers and therefore the best possible prognosis, so seeing a difference between groups getting one or the other drug likely will take longer than five years.

In fact, 13 percent fewer cancer deaths occurred among Arimidex users, but the trend wasn’t strong enough to say it couldn’t have resulted from chance alone, Buzdar said.

Nevertheless, “I don’t think you have to show a survival advantage to change practice habits,” because of Arimidex’s many other benefits, said Dr. Paul Goss, a Massachusetts General Hospital breast cancer expert who had no role in this study but has led others involving different aromatase inhibitors.

They include fewer cases of endometrial cancer, blood clots, hot flashes and vaginal bleeding and discharge than among tamoxifen users. Women on Arimidex had more joint pain and bone fractures, though the latter can be treated with other drugs.

Tamoxifen therapy for 5 years after surgery is currently the established treatment for postmenopausal women with hormone-sensitive breast cancer.

The new findings on Arimidex for postmenopausal women don’t change tamoxifen’s status as the drug of choice for breast cancer cases that occur before menopause, because aromatase inhibitors aren’t thought to be effective against them. Women whose tumors are not sensitive to the effects of estrogen also may be best off with tamoxifen.

The Associated Press and Reuters contributed to this story

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