Very few patients who've had cancer surgery end up participating in clinical trials to test new treatments, researchers have found, according to Reuters.

And those who do participate are younger and usually white, fueling concerns that new drugs may not fare as well once they hit the market because trial subjects don't match real-world users.

"Are you going to see the same benefits in the average patient?" said Dr. Monika Krzyzanowska, a cancer researcher at Princess Margaret Hospital in Toronto, Canada.

"Are the risks in the clinical trial truly reflective of the risk in the general population if the enrolled patients are younger and healthier?" added Krzyzanowska, who wasn't involved in the new work.

To get a sense of how often cancer patients enroll in clinical trials, Dr. Waddah Al-Refaie of the University of Minnesota in Minneapolis and colleagues tapped into a California cancer registry.

Only 1,566 of nearly 245,000 patients -- or about six of every 1,000 -- had participated in a trial, according to the report in the Annals of Surgery.

Whether that's because few trials were available, or because patients are reluctant to join them, or something else isn't clear.

The new findings are another illustration of the gap between real-world patients and those who participate in trials.

"Should we fix it? I think the answer is yes," said Krzyzanowska. "What the solution is is a much harder question to answer."

While there is no universal answer as to whether it would make sense for a particular cancer patient to enroll in a trial, she added, "patients should inquire about what clinical trials are available and figure out if there is something available for them."