Oct. 18 (Bloomberg) -- Breast-cancer patients may be urged to undergo genetic testing before starting therapy with the drug tamoxifen, under a proposal U.S. regulators are considering to help predict the risk of a relapse.

The Food and Drug Administration is asking outside advisers today to review studies that suggest women with a certain genetic profile may be more prone to relapse on tamoxifen, a standard treatment after surgery to remove a tumor. Tamoxifen, sold by several generic drugmakers, is often prescribed after diagnosis or to prevent breast cancer in high-risk women.

Cancers are among the first diseases for which researchers are exploring how genetics causes certain drugs to work better in some people than in others. Breast-cancer patients often have multiple treatment options and a high chance of survival. Genetic testing may be particularly useful in guiding therapy for the disease, which the American Cancer Society estimates strikes 213,000 U.S. women a year.

``It's a question of targeting the medicines and also targeting women in whom the medicines are expected to be effective,'' said Timothy Lash, an associate professor of epidemiology at Boston University, in an Oct. 16 telephone interview. ``Where women can be successfully treated, you want to optimize their treatment because you're hoping for a cure.''

Treatment Options

The FDA is asking a subcommittee of its advisory panel of outside drug experts to consider if scientific evidence warrants revising prescribing information for tamoxifen to recommend genotype testing for post-menopausal women before they are given the drug. Many women are already asking to be screened in clinical practice, Matthew Goetz, an assistant professor of oncology at the Mayo Clinic College of Medicine in Rochester, Minnesota, told the subcommittee today in Rockville, Maryland.

Alternative drugs work as well as tamoxifen, ``if not slightly better,'' and have different side effects, Goetz said.

The FDA approved newer medications for post-menopausal women based on studies that suggested the medicines were more effective than tamoxifen after surgery for breast cancer. The newer drugs, called aromatase inhibitors, include AstraZeneca Plc's Arimidex and Novartis AG's Femara. U.S. doctors usually choose to either prescribe these drugs on their own for five years or after a few years of tamoxifen therapy, Goetz said.

Generic Drug

Generic tamoxifen, given as a 20-milligram tablet once daily, costs about $38 for a one-month supply from the online pharmacy Drugstore.com. Thirty 1-milligram tablets of Arimidex cost $228, and 30 2.5-milligram tablets of Femara cost about $240.

The FDA approved tamoxifen, originally sold as U.K.-based AstraZeneca's Nolvadex, in 1977 to treat breast cancer, and later cleared it to help reduce cancer incidence in women at high risk of the disease. Almost 30 years later, regulators said understanding the influence of genetic traits on tamoxifen's effectiveness will allow doctors to weigh the risks and benefits of the therapy for certain patients.

``Tamoxifen is probably one of the most studied drugs in all of oncology,'' Goetz said.

AstraZeneca stopped making and selling Nolvadex tablets in June because demand had dwindled as more generic versions of the drug entered the market, a company spokeswoman, Kirsten Evraire, said today in an e-mail. The medicine is now made by several generic drugmakers, including Barr Pharmaceuticals Inc., based in Woodcliff Lake, New Jersey, and Teva Pharmaceuticals Industries Ltd., based in Petah Tikvah, Israel.

Genetic Differences

A federal recommendation for genetic screening to guide breast-cancer treatment may benefit makers of the tests, including Basel, Switzerland-based Roche Holding AG and Toronto- based TM Bioscience Corp. The tests cost about $100 to $600, more than an X-ray and less than a CAT-scan, researcher David Flockhart said.

About 7 percent of Caucasians carry an inactive copy of the enzyme CYP2D6, preventing the body from readily breaking down and excreting certain drugs, said Flockhart, a professor of medicine and genetics at Indiana University School of Medicine in Indianapolis. About 30 percent of all people have an underactive enzyme, he said.

Flockhart and his colleagues found that cancer patients whose CYP2D6 enzyme didn't effectively break down tamoxifen had a 60 percent chance of breast cancer recurrence after 10 years, compared with a risk of 20 percent to 25 percent in patients whose enzyme was intact. Their research was supported in part by Roche and TM Bioscience, Flockhart said Oct. 16 in a telephone interview.

Some studies have shown that women who take antidepressants such as Eli Lilly & Co.'s Prozac or GlaxoSmithKline Plc's Paxil for hot flashes during menopause also have worse outcomes on tamoxifen therapy. Flockhart said these data suggest the active ingredients in these antidepressants prevent the CYP2D6 enzyme from breaking down and using the cancer drug effectively. Many oncologists, as a result, have started prescribing different types of antidepressants, such as Wyeth's Effexor, for women taking tamoxifen, he said.

To contact the reporter on this story: Catherine Larkin in Washington at clarkin4@bloomberg.net.

Last Updated: October 18, 2006 12:04 EDT