On the trail of a killer

At some point in their lives, most Canadians will be encouraged to get screened for cancer, whether it’s colon, breast or cervical, to catch early signs of disease. For the leading cancer killer, lung cancer, no screening program exists. Even so, early detection is crucial: just 16 per cent of Canadians diagnosed with lung cancer will be alive five years later, but if it’s treated early, that number can jump to over 77 per cent. Experts are working on new ways to catch the disease, which could save countless lives.

Doctors have tried screening for lung cancer with everything from chest X-rays to sputum tests (which check spit under a microscope). So far, none have been proven to dependably find it early enough to make a difference. For that reason, notes the American Cancer Society, major medical bodies haven’t recommended they be used to screen the public—not even smokers. Chest X-rays are “probably too insensitive to pick up lesions small enough to treat,” says Dr. John Goffin, a lung cancer expert at McMaster University. And this type of cancer develops so quickly that, once it’s caught, it’s often too late.

In the U.S., a large clinical trial is under way comparing two potential screening methods: chest X-ray and spiral CT scan (an X-ray procedure that takes images while rotating around the body). With over 50,000 current or former smokers participating, the trial should help determine whether one of these methods can help reduce lung cancer deaths. But that’s just one piece of the puzzle. Because screening is generally performed on people who are symptom-free—and screening everybody, even all smokers, would be prohibitively expensive—defining a target population is important. In Canada, a team is looking at “how to define risk” for lung cancer, says the B.C. Cancer Agency’s Dr. Stephen Lam, the study’s principal investigator (with Dr. Ming Tsao of the Ontario Cancer Institute). According to Goffin, a participating researcher, using low-cost methods like questionnaires, breathing tests or blood work could help doctors know who’d benefit from more expensive screening, like CT scans. “If you have to screen 50,000 people to find one cancer, it’s not a good use of resources,” says Dr. Garth Nicholas, an Ottawa-based medical oncologist who’s participating. “We’re trying to see, can we identify with cheaper tests, a group of high-risk people in whom we’re more likely to find something.” As of February, over 1,900 people had enrolled, with 26 cancers identified.

Beyond that, new tests for lung cancer are being developed. According to Dr. John Robertson of the University of Nottingham, solid cancer tumours “make abnormal proteins” that trigger the immune system. This antibody response can be an early flag of cancer, he says. Robertson’s research has been used to develop a blood test that, according to him, will help detect lung cancer “up to five years earlier.” Created by the spinoff company Oncimmune, the test, called EarlyCDT-Lung, launched in the U.S. this month; it should soon be available in Canada, too. (EarlyCDT-Lung costs $475 through a doctor’s office, according to Robertson.) The blood test is “an aid to detection; it isn’t diagnosis,” he says: for every six high-risk smokers—someone with a five per cent chance of developing lung cancer within five years—who test positive, one will have lung cancer. It could be a powerful tool in helping doctors define who’s at highest risk for the disease.

In the future, genetic testing might help further define who’s at risk. About 15 per cent of men and 53 per cent of women who develop lung cancer are “never smokers,” according to a recent U.S. study. It also found that about 30 per cent of lung cancer patients who’d never smoked shared a genetic variation. “We never had proof of a genetic link before in never smokers,” says lead investigator Dr. Ping Yang of the Mayo Clinic, noting the discovery may eventually provide new targets for treatment. Genetic testing, she says, is a long-term goal.

Despite these advances, the population at highest risk for lung cancer is well-known: smokers. Alongside prevention, to save lives, early diagnosis of the disease is crucial. With about 1.2 million people dying of lung cancer each year—more than colorectal, breast and prostate cancer combined—it can’t happen fast enough.