(FORTUNE Magazine) – "I wondered if it would be inevitable" that I would get breast cancer, says a young brunette in a dramatic TV ad that has been airing in Denver and Atlanta for the past six months; soon the campaign will go nationwide. But this is no public-service pitch. Rather, it's an audacious effort by Myriad Genetics, a $54-million-a-year Salt Lake City biotech company, to convince women to take its test for a genetic predisposition to the disease.

Direct-to-consumer advertising for medical products isn't new. But using TV spots to market a genetic test --with all its attendant medical, psychological, ethical, and legal complexities--is. Insurers and HMOs, as well as doctors and breast cancer advocates, worry that the commercials will unnecessarily frighten women. They also fear that the ads will compound the problem of rising health-care costs (see "The Breaking Point"), especially if such campaigns become a standard marketing tactic for genetic tests.

There is little doubt that Myriad's commercials are effective. The company says calls to its referral hotline rose by a factor of 40 after the ads began airing. The problem is that very few women need to be tested. Only 5% of breast cancers are thought to have a genetic link. The mutations Myriad screens for occur in, at most, one out of 400 women (though the figure is one in 50 for Ashkenazi Jews). Likely candidates should have a significant family history of breast or ovarian cancer, something that Myriad's ads don't make explicit. The ads also don't mention any treatments for women who test positive; these range from more frequent mammograms to a preventive double mastectomy.

The company says its marketing campaign, which also includes radio and print ads, was designed to avoid scaring women. But Judy Mouchawar, director of cancer genetic services at Kaiser Permanente of Colorado, notes that since the ads began airing in Denver, the number of low-risk women referred for pretest genetic counseling has increased significantly. Nationwide, 25% of all women referred for testing are at low risk for the mutation. And that's without Myriad's ads calling widespread attention to the problem, says Steven Bloom, vice president for marketing at Inflexxion, a Boston health information company. (Inflexxion has developed a CD-ROM to educate women and their families about genetic testing issues with breast cancer.) The fear that women will be inappropriately tested has led Dr. Edward Hill, board chairman of the American Medical Association, to voice "grave concerns" with Myriad's campaign.

As for insurers, it's no secret why they're worried: A DNA screen costs $2,800, and most insurers require pretest genetic counseling--at $200 per hour. Counseling will weed out most low-risk women, but there are only 350 counselors nationwide. That means long waits that will get longer as Myriad's campaign goes national. "As we learn more about the genetics of common diseases, and more tests begin to be marketed, I think we are going to be in real trouble in terms of how to provide services," Mouchawar says. The future is coming fast. Last month, Myriad claimed it had discovered a gene linked to depression. --Jeremy Kahn