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New Drug, Faslodex, Shows Promise for Treating Advanced Breast Cancer (dateline December 25, 2000)

Two recent studies presented at the 23rd Annual San Antonio Breast Cancer Symposium found that an experimental drug called Faslodex (generic name, fulvestrant) may help treat women with advanced breast cancer who have become resistant to the drug, tamoxifen (brand name, Nolvadex). According to the researchers, Faslodex appears to slow the progression of cancer and shrink the size of tumors in some women. Herman Kattlove, MD, a medical oncologist with the American Cancer Society, calls the study results promising and says that Faslodex has the potential to become a valuable addition in the management of advanced breast cancer.

In both studies, researchers compared the effectiveness of Faslodex to Arimidex (generic name, anastrozole), another drug used to treat advanced breast cancer. In the North American trial involving approximately 400 women with advanced breast cancer, lead researcher Kent Osborne, MD, director of the breast center at Baylor College of Medicine, and his colleagues found that both Faslodex and Arimidex were effective at slowing the progression of cancer. Cancer did not progress for an average of 5.5 months among the women on Faslodex compared with 3.5 months for the women who took Arimidex. The researchers also found that tumor shrinkage was similar among the women, regardless of which drug they took.

In all, approximately 18% of the women responded well to either Faslodex or Arimidex. However, most of the women who took Faslodex were able to take the drug for approximately 19.3 months before they became resistant to it, while the women who took Arimidex became resistant to the therapy in approximately 10.5 months.

According to Dr. Osborne, Faslodex appears to be another option for women with advanced breast cancer. Another study presented at the San Antonio Breast Cancer Symposium also found Faslodex to be equal to Arimidex in helping to slow cancer growth and shrink tumor size. Both drugs were generally well-tolerated and side effects were similar. The most common side effects of Faslodex and Arimidex were hot flashes and stomach upset.

Both studies show that Faslodex appears to be effective for women who have become resistant to tamoxifen, said Dr. Osborne. Since all three drugs (Faslodex, tamoxifen, and Arimidex) treat estrogen-sensitive breast cancer in different ways, Dr. Obsorne said that the three drugs may be used effectively one after another. Further research will help determine the proper order in which these drugs would be most effective for women with advanced breast cancer.

Many breast cancers contain estrogen receptors within their cells. To survive and reproduce, these cancers depend on the hormone estrogen. Researchers have found that using hormonal agents that prevent estrogen from binding to these receptors in cancer cells helps slow the growth of cancer. All three drugs (tamoxifen, Arimidex, and Faslodex) are hormonal therapies and each interferes with the binding of estrogen in different ways.

How the Drugs Treat Breast Cancer

Tamoxifen Blocks estrogen from estrogen receptors in breast cancer cells.
Arimidex Prevents production of estrogen in adrenal glands.
Faslodex Destroys estrogen receptors in breast cancer cells.

Nearly 183,000 new invasive cases of breast cancer will be diagnosed by the end of 2000 and many of those cancers will have already progressed to advanced stages before they are detected. Recently, several studies have shown promising results with new drugs or drug combinations that may help slow the progression of breast cancer and help women with advanced breast cancer live longer. Click on the links below to read about other recent studies involving the treatment of advanced breast cancer.

Additional Resources and References