Personalized medicine to guide prostate and other cancer treatment decisions is advancing as new tests for the genetic signature of tumours come on the market, Canadian oncologists say.
This week, doctors attending the American Urological Association meeting in San Diego heard about the launch of a new prostate cancer test that analyzes multiple genes from a biopsy sample and scores it based on aggressiveness.
"The problem is historically a small proportion of the slow growing types can behave aggressively and conversely many of what we think are the faster growing types still never harm the patient," said Dr. Neil Fleshner, head of the urology division at Toronto's Princess Margaret Cancer Centre.
Traditionally, doctors based their advice to treat with surgery, radiation or both based on the size of the tumour and how the cancerous cells look under the microscope.
Researchers said the results suggested Genomic Health's Oncotype DX Genomic Prostate Score could triple the number of men thought to be at such low risk for aggressive disease and who could be safely watched. Conversely, the $3,820 US test also suggested some tumours were more aggressive than previously thought.
Don Konantz of Vancouver, 50, discovered he had an abnormally high prostate specific antigen or PSA score during a routine checkup 2½ years ago. He had surgery to remove the prostate and tumour, radiation and drug treatment.
"There's no question that there are a lot of side-effects," Konantz said. "The drugs dramatically affect my body chemistry. The radiation is very tough and the surgery monkeys around with your insides."
Konantz hopes the test could reduce overtreatment of prostate cancer with surgery.
"Unless you can be sure your biopsy has hit the most aggressive part that's in the prostate, you can't be sure" how accurate your risk estimate is, said Dr. Eric Klein, chief of urology at the Cleveland Clinic, who led early development of the Oncotype prostate cancer test.
Under conventional methods, 37 of the 395 men who were scheduled to have their prostates removed would have been determined to be low risk and good candidates for watchful waiting. Adding the gene test pushed up the number in that group to 100 men.
The results still leave a lot of uncertainty because it doesn't offer a zero or 100 per cent answer on whether a cancer is unlikely to harm a man in his lifetime, Fleshner said.
A similar test for breast cancer is available under some provincial and territorial health plans when indicated. Another for colon cancer exists and one for lung cancer is in development, said Dr. Malcolm Moore of Princess Margaret Cancer Centre.
"We can use this genetic information to give patients much more precise estimates about what their risks are," Moore said. "They provide a little bit more precision, maybe 10 per cent, over what we have presently."
Moore said the new genome tests have three main advantages:
- More accurately predict risk of recurrence.
- Tailor drug treatments to the tumour's genetics if it suggests the usual treatment won't work well, rather than relying on what's worked best before based on averages alone.
- A genetic mutation could be identified in the tumour that suggests a better treatment.
"I think a lot the excitement around these genetic tests isn't so much that the tests themselves of the moment are good," said Moore. "It's that it kind of points the way forward to the way we're going to be doing things in five or 10 years."