This article was first published in The Montreal Gazette.
Lung cancer remains the No. 1 cancer killer in the country. Every year, lung cancer kills far more women than breast cancer and far more men than prostate cancer. Its five-year survival rate is a depressingly low 19 percent, compared to breast cancer (88 percent) or prostate cancer (93 percent). There is, however, something we can do to improve lung cancer outcomes. The problem is we just don’t do it.
The key to reducing cancer deaths is effective screening. Screening for cervical cancer (with Pap tests) and colorectal cancer (with colonoscopies and now with FIT testing) has led to dramatic reductions in both of these cancers. The point is to catch a pre-cancerous lesion and remove it before it can transform into a more aggressive cancer and metastasize through the body. Unfortunately, not all cancers are amenable to screening. For example, screening for prostate cancer with PSA is more complicated than it might seem.
Likewise, screening for lung cancer is not very easy. Intuitively, you would think that X-rays should catch lung tumours early when they are still small and easily removable. But data from studies like the PLCO trial have shown that regular chest X-rays do not reduce lung cancer mortality. In fact, most guidelines recommend against using chest X-rays to screen for lung cancer because, apart from being largely ineffective, there are also significant downsides. Cost and repeated radiation exposure are obvious negatives. But the real danger associated with X-rays is that of over-diagnosis. What can seem like a mass on an X-ray can turn out to be nothing after more scans and biopsies. The rate of these false positives can be quite high. In the National Lung Screening Trial, the false positive rate with annual X-rays was nearly 95 percent.
The past few years have shown that CT scans may be a better option. The National Lung Screening Trial compared low dose CT scans to standard X-rays and found that CT scans picked up more cancers and reduced lung cancer deaths from 309 to 247 deaths per 100,000 person-years. While the rate of false positives was still high (over 96 percent), the mortality reduction convinced many people that screening with yearly CT scans was worth the effort.
Critics have pointed out that the reduction in mortality is relatively small, that the false-positive rate with CT scanning is still very high and that CT scans deliver even more radiation than X-rays. But even if you account for the radiation delivered by CTs, you would still pick up 108 lung cancers for every one cancer caused by the radiation. In fact, simulation studies suggest that if everyone eligible for lung cancer screening got yearly CT scans, you prevent just over 12,000 lung cancer deaths every year.
Guidelines recommend annual screening for three consecutive years with low-dose CT scans for adults ages 55 to 74 (U.S. guidelines say 80) who have a history of heavy smoking and currently smoke or quit less than 15 years ago. Heavy smoking is usually defined as a smoking history of 30 pack-years (one pack a day for 30 years, two packs a day for 15 years or three packs a day for 10 years).
Unfortunately, a U.S. study found that seven out of eight adults who would qualify for lung cancer screening do not get it. People have suggested that there is a bias against smokers, but I suspect most people are simply not aware of the guidelines.
Given how much attention we pay to breast cancer and prostate cancer screening, it is sometimes surprising we do not talk about lung cancer screening more since lung cancer is actually more lethal.
It would be good if people were aware of the guidelines and got screened if they meet the criteria. But it would be even better if they stopped smoking.
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