p16 genetic testing appropriate in highly limited situations

April 1, 2005

New Orleans — When it comes to p16 genetic testing for melanoma, practicing dermatologists should realize only a very small percentage of patients are appropriate candidates, and even for those who are, the testing should only be undertaken when the patient can receive the necessary pre- and post-test genetic counseling services, said Sancy A. Leachman, M.D., Ph.D., at the 63rd Annual Meeting of the American Academy of Dermatology here.

"If you consider all of the patients who present with melanoma to the average dermatologist's office in the community, only about 10 percent would be considered candidates based on having a strong enough family or personal history," says Dr. Leachman, medical director, Huntsman Cancer Institute Familial Melanoma Research Clinic, University of Utah.

Identifying candidates Topping the list of potential candidates for p16 genetic testing is any person who is a first-degree relative of a proven p16 mutation carrier.

All other candidate categories pertain only to persons affected by melanoma. The underlying reasoning for including only those individuals is that if the p16 test comes back negative and the family's p16 status is unknown, it is unclear whether the negative result for that individual means they are an unaffected member of a p16-carrying family or of a family that carries a melanoma-causing mutation other than p16.

"Although about 10 percent of the melanoma population would be candidates for p16 genetic testing, only about 25 percent of those individuals are going to end up being p16 mutation carriers. The flip side is that about 75 percent are going to have some other mutation that is yet to be identified," Dr. Leachman notes.

Persons with melanoma who deserve consideration for p16 testing are those with:

If a candidate for p16 testing is identified, that individual should be referred to a facility with an ongoing research protocol.

"Referral is important because the research program will likely have the capacity to not only identify p16 mutations but other new evolving genes," Dr. Leachman explains.

If that is not an option, the patient should be referred to a clinical genetic testing center where both testing and counseling services would be available. Prior to p16 genetic testing, all patients need to receive a thorough and complete informed consent that includes education about the risks, benefits and limitations of the testing, along with discussions of confidentiality, genetic discrimination issues, and psychological implications.

Patient education Once a person decides to undergo testing, it is also critical to have a genetic counselor available who can discuss the results accurately and in an understandable manner, and who will be able to answer any questions the patient has.

"Patients need to have a clear understanding of all of the ramifications of testing so that they can make an informed decision about whether or not to proceed, and they also need to have the results delivered to them in appropriate fashion. It is unlikely that many dermatology practices in the community have the resources and capability to provide the necessary counseling services in their offices, and so unless there is a genetic counselor nearby, dermatologists may want to refer to a cancer center," Dr. Leachman says.

She also reminds her colleagues that the p16 mutation is associated with familial pancreatic cancer, and that association provides another reason for considering p16 testing in appropriate persons.

"Knowing that a person is ap16 carrier is important from the standpoint of enabling appropriate melanoma prevention and surveillance strategies, but also for allowing that individual to decide about enrolling in a pancreatic cancer screening trial," Dr. Leachman says.