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U.S., U.K., Researchers Tout Breast Cancer Drug at San Antonio Conference

Posted on: Thursday, 9 December 2004, 15:00 CST

Dec. 9--For three decades, tamoxifen has been the drug of choice to keep breast cancer from returning in women who were treated for the disease.

But American and British researchers at a San Antonio conference said Wednesday that a new drug called anastrozole clearly is better than tamoxifen, and should be the first drug used with most women who have breast cancer.

Data presented at the San Antonio Breast Cancer Symposium, and published at the same time in the journal the Lancet, indicated that postmenopausal women who took anastrozole were less likely to have their breast cancer return or to see it spread.

More than 2 million women living in the United States have been treated for breast cancer, according to American Cancer Society estimates.

Dr. Anthony Howell of Christie Hospital in Manchester, England, the principal investigator in a study involving 9,300 women, said anastrozole cut the recurrence of cancers by 70 percent, compared to a 50 percent reduction in women who took tamoxifen.

In addition, women taking anastrozole had fewer strokes, blood clots and uterine cancers than women who took tamoxifen.

"It is more effective and less toxic," Howell said of the new drug.

"In other words, you can avoid one in four recurrences by starting with the newer pill than by starting with tamoxifen," said Dr. Aman U. Buzdar, a professor at the University of Texas M.D. Anderson Cancer Center in Houston.

Women who took anastrozole did have higher rates of osteoporosis, reflected in a higher rate of spine fractures, Howell said. But he noted other studies, also presented Wednesday, that showed drugs called bisphosphonates were effective in countering bone loss.

Anastrozole, sold under the brand name Arimidex, is one of a new class of drugs called aromatase inhibitors. It works by interfering with the body's production of estrogen, a hormone that feeds the most common type of breast tumors. Tamoxifen works by blocking the effect of the hormone instead.

For the past three decades, postmenopausal women with hormone-sensitive breast cancer were routinely given tamoxifen for five years after surgery.

The current study began in 1996 and enrolled 9,366 women from 21 countries in a comparison of the two drugs.

Preliminary results published over the past three years suggested that aromatase inhibitors were more effective than tamoxifen. But the newest results reflect five years worth of data and are the long-term numbers that doctors want to see before changing the standard of care, said Dr. Lawrence Wickerham, associate chairman of the National Surgical Adjuvant Breast and Bowel Project.

The breast and bowel project is a study group that was not involved in the drug study.

"The five-year data adds to that credibility, and particularly the lack of additional toxicity surprises us," he said. "This drug works better and has less life-threatening side effects."

In a related study, Austrian and German doctors found that women who switched to anastrozole after taking tamoxifen for two years also did better than women who continued on tamoxifen for five years.

It showed women who switched had a 40 percent less chance of the cancer returning, one doctor said.

The study "provides very useful information that these women should now go and talk to their doctors," Buzdar said. "By switching them after two or three years, there is now quite convincing data that you cut down the risk of recurrence substantially in these patients instead of completing five years on tamoxifen."

The 27th annual symposium, sponsored by the San Antonio Cancer Institute attracts 6,500 doctors, scientists and advocates from 80 counties. It is the largest yearly scientific meeting on breast cancer in the world.

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Source: San Antonio Express-News

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