Cancer campaigners have applauded actress Angelina Jolie for going public about her double mastectomy, but warned women against rushing out to be tested for the gene mutation that threatened her life.
Jolie's BRCA1 mutation is rare in the overall female population, they said, and tests at a US laboratory that controversially claims the patent rights to the gene are expensive.
"We don't want everybody to go out and say, 'I want this test,'" said Otis Brawley, chief medical officer of the American Cancer Society. "We want people to think about what their family history is, and to talk to their doctor," who might refer them to a genetic counsellor to determine if testing is necessary, Brawley said.
"Women who have firstdegree relatives - that is, a sister or a mother - who had breast or ovarian cancer at a young age should especially have these conversations," he said.
Los Angeles-based surgeon, author and leukaemia survivor Susan Love added: "All women should not be tested for this gene. It is not that common.
"The people who should consider being tested are the ones who have had a lot of breast or ovarian cancer in their families."
Jolie's mother died of ovarian cancer at the age of 56.
Writing in The New York Times on Tuesday, the 37-year-old Lara Croft: Tomb Raider star and UN humanitarian activist said genetic tests had established that she was carrying the "faulty" gene known as BRCA1.
"She's very brave to speak out," said Katherine McLane, vice president for communications at Livestrong, the cancer charity founded by cyclist and cancer survivor Lance Armstrong before his fall from grace in a doping scandal.
But McLane voiced hope that Jolie's experience would also generate "more attention about affordable health care for all women".
Jolie, one of Hollywood's highest-paid stars, decried the fact that a BRCA1 test - which costs more than US$3,000 in America - is out of reach for many women around the world.
Myriad Genetics is the only US lab that offers the test, and it is at the heart of a US Supreme Court battle over its claim of patent rights to BRCA1 and BRCA2. A ruling is expected next month.
On the Nasdaq stock market on Tuesday, shares in Myriad Genetics leapt four per cent on news of Jolie's article to US$34.45, its best level since mid-2009, before easing back.
"We strongly believe appropriate use of many of our diagnostic tests can help reduce illness, hospitalisations and other costly interventions, and potentially lower health care costs," Myriad Genetics declared in a statement.
It declined to say whether it was the lab that tested Jolie.
Several facilities in Europe offer the same test, according to the American Civil Liberties Union, which is challenging Myriad Genetics' patent claim in court.
Overall, cancer death rates in the US have been declining among both men and women since the early 1990s, according to the National Cancer Institute, a US government agency.
But while 12 per cent of all US women will develop breast cancer at some point, the chances are five times greater for the few with a BRCA1 or BRCA2 mutation, it says on its website (www.cancer.gov ).
Both mutations can also turn up in men, increasing their risk of breast, pancreatic, testicular and prostate cancer.