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Breast cancer drugs go head-to-head in new trials

Last Updated: 2003-05-29 14:02:18 -0400 (Reuters Health)

NEW YORK (Reuters Health) - AstraZeneca Plc. said Wednesday it has launched new North American and European clinical trials to compare the breast cancer drug Arimidex (anastrozole) to the tried-and-true tamoxifen for patients with early-stage breast cancer.

Tamoxifen works by blocking the effects of estrogen on tumor cells. The drug, produced under the name Nolvadex by AstraZeneca, is the most widely prescribed drug for breast cancer treatment.

Anastrozole -- which is a member of a newer class of drugs called aromatase inhibitors -- decreases the overall amount of estrogen in the body. Both tamoxifen and aromatase inhibitors only work in patients who have breast tumors that are hormone receptor-positive, meaning that estrogen fuels the cancer growth.

Early research suggests Arimidex may not have side effects associated with tamoxifen, such as an increased risk of blood clots or endometrial cancer, although other side effects such as bone loss are a concern.

Arimidex is approved in the U.S. and Europe as a first-line treatment for advanced postmenopausal breast cancer and as an adjuvant treatment for postmenopausal women with estrogen receptor-positive early breast cancer. Nolvadex (tamoxifen) just lost patent protection and faces competition from a number of recently approved generic competitors.

One new study comparing the two will be conducted at 150 centers in the U.S. and Canada and is sponsored by the clinical trial cooperative the National Surgical Adjuvant Breast and Bowel Project (NSABP), AstraZeneca said.

The study, called B-35, will compare five years of Arimidex treatment to tamoxifen in preventing the development of invasive breast cancer in 3,000 post-menopausal women with ductal carcinoma in situ (DCIS) who have undergone lumpectomy and radiation therapy. DCIS is an early stage of breast cancer involving only the cells lining the milk ducts.

The second five-year trial, called the International Breast Cancer Intervention Study-2 (IBIS-II), will compare Arimidex to tamoxifen in 4,000 patients with DCIS who have undergone lumpectomy with or without radiation therapy. It will also test Arimidex versus placebo in 6,000 post-menopausal patients at high-risk of developing breast cancer.

The study is being sponsored by the recently established charity Cancer Research UK, AstraZeneca said.

"Arimidex offers postmenopausal women with hormone-sensitive breast cancer an alternative to tamoxifen," Dr. Joseph Purvis, executive director of clinical development at AstraZeneca Pharmaceuticals, said in a statement. "And through these two very important clinical trials we will learn much more about the effectiveness of Arimidex in women who have not yet developed invasive breast cancer."

AstraZeneca is supplying the drug for both clinical trials and financially supports both NSABP and Cancer Research UK.

Other trials have looked at how the two drugs stack up when it comes to treating breast cancer. A multi-year trial known as the Arimidex, Tamoxifen Alone or in Combination (ATAC) trial is following more than 9,000 women who were treated with the drugs either with or without radiation after undergoing breast cancer surgery. Early results from that trial were reported last year.

For more information about the new trials, visit the NSABP Web site at www.nsabp.pitt.edu, the National Cancer Institute's Web site at http://cancertrials.nci.nih.gov, or Cancer Research UK's site at www.cancerresearchuk.org.

Copyright 2002 Reuters.