(Courtesy of the American Cancer Society via Getty Images)

 This year, more than 26 thousand Canadians will be diagnosed with lung cancer and close to 21 thousand will die of it. That's according to the Canadian Cancer Society. A controversial new set of screening guidelines just published in the Canadian Medical Association Journal say doctors should do more to save lives. 

The guidelines say adults age 55 to 74 who are at high risk should be screened for lung cancer once a year for up to three years. By high risk, the guidelines mean men or women who are current heavy smokers or former heavy smokers who have quit within the past 15 years. Heavy smoking is defined as smoking on average a pack of cigarettes a day for at least 30 years.  

The guidelines come from the Canadian Task Force on Preventive Health Care  established by the Public Health Agency of Canada to develop guidelines to help prevent serious conditions like cancer and heart disease.  The idea behind the guidelines is to detect lung cancers when they're tiny and perhaps more curable.

They say current or former heavy smokers should have a low dose CT scan of the chest once a year for up to three years.  CT scans are incredibly detailed. Plain x-rays can identify lung cancers the size of a dime; low dose spiral CT scans can find ones the size of a grain of rice. In the past, doctors recommended an annual chest x-ray.  Unfortunately, that approach did not save lives through early detection of lung cancer  which is why we no longer recommend them.  Two studies cited in the CMAJ article found that compared to x-rays, low dose CT scans found more cancers and saved more lives.  Low dose CT scans also detected more early stage lung cancers when they're curable.

Some say the new guidelines put Canadians at risk. The National Lung Screening Trial which was cited by the article  found that for every 1000 people who get three low dose CT scans in three years,391 will have at least one positive scan.  Of those, 40 will have confirmed lung cancer, but 351 will have a false positive result. That means the CT scan finds something that looks like a cancer  but further testing shows no cancer. The confirmatory tests are invasive; they include bronchoscopy in which the patient is sedated and a bronchoscope is passed through the mouth and into the bronchial passages  as well as biopsies.  

In the study I just mentioned, three out of every 1000 people screened for lung cancer with low dose CT scan had a major complication from invasive testing, and one per 1000 died as a result of the invasive test.  There's also the risk of radiation exposure from the CT causing a fatal cancer at a rate of about one in 2,000.  

The new guideline says not every smoker or ex-smoker should be screened for lung cancer. Screening with periodic CT scans is not recommended for patients younger than 55 or older than 74 because there's no proven benefit in those age groups.  As well, if you're not a heavy smoker (one pack a day for at least 30 years), your risk of lung cancer is lower and therefore the benefit of screening isn't high enough to justify the risk.  By the same logic, if you quit more than 15 years ago  no matter how much you smoked back then  your risk of lung cancer has dropped to the point at which screening isn't worth the risk.

These new recommendations are highly significant given society's attitude toward smokers.  I'm sure some people would question spending public money to do expensive CT scans to screen for lung cancer given that 85 per cent of the 26,000 lung cancers diagnosed in Canada each year are caused by smoking.  

I have two answers to that.  First, we spend a lot of public money treating other diseases associated with diet, weight and alcohol consumption.  I'm not sure it's fair to single out smoking.  Second, a lot of the people who are eligible for screening are ex-smokers who quit in the past fifteen years.  For that, I think we owe it to them to look for cancers that are potentially curable.  As for current smokers, screening them for lung cancer provides an excellent opportunity encourage them to quit.  I'm all for it.