With a speed so rapid that many medical experts are taken aback, genetic tests that can tell if a person is likely to get cancer are entering the marketplace.
Those in favor of testing say that people have a right to know if they are at increased risk and that it would be unethical to deny them that knowledge. They say that people who harbor cancer genes may be helped by undergoing frequent screening for cancer so they could get early treatment.
But opponents say it is too soon, that the tests are still research tools, that it is not clear if patients will be helped or harmed by knowing their medical futures, and that in some cases it is not clear how to interpret the test results.
Another gene points to an inherited predisposition to any of a variety of cancers, including breast cancer and brain tumors.
The tests, which cost $800 for the first family member and $250 for each additional member, involve analyses of genes obtained from blood samples or, in the case of the melanoma gene, from swabbings of the inside of a patient's cheek.
The genes were discovered only recently. The melanoma gene was reported in September, for example, and the breast cancer gene in October. And some researchers say they are only beginning to understand the consequences of inheriting one of these genes.
Dr. Francis Collins of the National Institutes of Health in Bethesda is the director of the Human Genome Project, the federal effort to map the entire human genetic sequence. Dr. Collins said the effort to market the genetic tests "is alarming."
"We are talking about treading into a territory which the genetics community has felt rather strongly is still research," Dr. Collins said. "Unanimously, the professional genetics community, the Human Genome Council and the National Breast Cancer Coalition have stated that these tests should not now be made available."
But Fred C. Follmer, the chief financial officer of the Preferred Oncology Network in Atlanta, a national association of hundreds of private cancer specialists, said the critics "had better get ready for this."
The tests, he said, are already here. His group has signed an agreement with OncorMed Inc., a biotechnology company in Gaithersburg that will perform the tests.
OncorMed has also advertised to doctors outside the network that it can now test patients for cancer genes.
Members of the oncology network will begin offering the tests within the next month.
Dr. Timothy Triche, the chief executive officer at OncorMed and the chief of pathology at Children's Hospital in Los Angeles, said that he recognizes the controversy but that it is too late to stop the testing.
He said that because one test in particular, the one for the breast cancer gene, has become so contentious, the company will initially refer women who want it to a consortium of doctors at medical centers.
But Dr. Triche added that although OncorMed may be the first, it is far from the only company interested in marketing the tests.
He predicts it will not be long before doctors begin using the tests routinely. "With time, of course, this will be available to every physician," he said.
Computer programs that OncorMed has developed can help pick out those whose family histories indicate they may carry cancer-causing genes, Dr. Triche said. Then, those who are identified can be offered genetic tests. If they inherited cancer genes, the doctors would urge them to be screened for cancer "on a much more regular basis at a much earlier age," than others without the genes, Dr. Triche said.
But some who have done the research leading up to the gene discoveries are wary.
Dr. Barbara Weber, a breast cancer researcher at the University of Pennsylvania School of Medicine, says that the gene, called BRCA1, is large with many possible mutations.
If the investigators find a mutation they have not seen before, they cannot immediately tell whether that mutation causes cancer.