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Drug Offers Progress on Cancer Study in 20 Nations Tracked 9,000 Women

Posted on: Friday, 10 December 2004, 12:00 CST

A class of hormone-blocking drugs called aromatase inhibitors was more effective in preventing breast cancer recurrence in women past menopause than was tamoxifen, a medication now prescribed by many doctors, researchers have reported.

The authors of the study, published online Wednesday in the British medical journal The Lancet, said the findings suggested that aromatase inhibitors should replace tamoxifen as the first line of treatment for postmenopausal women with breast cancer.

But other experts said it was too early to tell if treating women with aromatase inhibitors from the outset was better than using tamoxifen first, followed by the newer drugs.

The researchers tracked more than 9,000 women in 20 countries for roughly five years. They found that women who took the drug Arimidex, one of three aromatase inhibitors on the market, had a lower rate of recurrence and fewer side effects than those who used tamoxifen.

"I think tamoxifen is going to have a difficult time from now on," said Dr. Anthony Howell, the lead author of the study and a professor of medical oncology at the University of Manchester in England. The study was financed by AstraZeneca, the London-based maker of Arimidex. Howell is listed in the medical journal as having received speaking fees from the company.

Several experts, while saying that the new findings were encouraging, called the authors' conclusions premature. They said that other research suggested that many women might gain a slight advantage by taking the two drugs sequentially, tamoxifen for two to three years followed by an aromatase inhibitor. And it will be at least another year before studies are completed that directly compare an aromatase inhibitor alone with a combination of the two drugs.

The United States' leading group of cancer specialists recommended last month that women take an aromatase inhibitor at some point in their treatment, but said it was not clear whether taking the drug from the outset was better. Those guidelines will not change as a result of the new study, said Dr. Eric Winer, who was chairman of the technology assessment panel for the American Society of Clinical Oncology, which issued the recommendations.

"The unanswered question at the moment is whether aromatase inhibitors should be used as an initial therapy or whether they might work even better if tamoxifen is given first for some amount of time," said Winer, who is also director of the breast oncology center at the Dana-Farber Cancer Institute in Boston.

"Many of us feel it is equally reasonable to take tamoxifen followed by an aromatase inhibitor," he said.

Winer has received research funding from pharmaceutical companies that manufacture aromatase inhibitors, including AstraZeneca.

Because the women in the new study had early cancers, and were followed for only five years, there was no difference in survival rates. But the group that took Arimidex reduced the chances of their cancer spreading by 14 percent and were 42 percent less likely than women on tamoxifen to develop a tumor in the other breast. They also suffered fewer side effects like blood clots, hot flashes and endometrial cancer, a cancer of the uterus.

Other aromatase inhibitors approved for use in the United States are Femara, made by Novartis, and Aromasin, made by Pfizer.

Tamoxifen blocks tumors from feeding off estrogen. Drugs like Arimidex inhibit aromatase, an enzyme used by bodily tissue to make estrogen, but they do not stop ovaries from making estrogen. Aromatase inhibitors are prescribed for patients past menopause, after their ovaries stop making estrogen.

Source: International Herald Tribune

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