A post on About.com makes the case that screening the higher risk population of just those people 55-75 with a significant smoking history, as was done in the influential National Lung Cancer Screening Trial (NLST) published last year in the New England Journal of Medicine, would miss nearly 3 of 4 lung cancers even as this effort improves lung cancer survival by 20% in the screened population. This piece implies that broader screening across of a wider range of ages and smoking history would be appropriate in order to detect more lung cancer and improve outcomes.   So let me make two points.

1) I am a proponent of lung cancer screening for an appropriate population and think it's underutilized now.

2) It is categorically incorrect to presume that broadening screening to a wider population will lead to better outcomes.

Why?

The NLST paper was among the most important developments in lung cancer in recent years, and it does document a 20% improvement in overall survival in the screened population, who had a significant risk for lung cancer as defined by being old enough to have a greater probability of developing cancer, young enough to not have a high probability of competing risks limiting the ability to be treated for lung cancer, and enough of a smoking history that nodules found by screening would have a real probability of representing cancer vs. a benign finding like inflammation, infection, prior scarring, etc.  We also know that screening for lung cancer with chest CT scans detects many nodules that are not cancer, and this is associated with additional scans, a significant risk of pursuing invasive tests to chase down findings, and significant anxiety in those affected.  There is also some potential risk from the radiation administered with scanning, which we want to be minimal, and which is undefined over the long term.

Screening for any cancer makes sense if you can focus on the people with a high enough risk that the benefit exceeds the risks.  But there are risks, and not just the cost of doing CT scans tens of thousands of additional people every year (though that isn't trivial).  The more broadly screening is applied to a group at low risk for actually having cancer, or not being fit enough to pursue treatment for a cancer detected early (such as a 79 year-old with significant heart disease), the more likely screening will deliver the negative consequences without the benefits.  The yield of screening will decline dramatically if it is applied to younger patients and never-smokers or those with a minimal smoking history, and there is a far greater probability that any suspicious findings will entail the repeat scans, interventions, and anxiety without sufficient probability of a real cancer to counterbalance those factors. 

It is absolutely true that more lung cancers could be detected if screening is pursued for a very broad population, but the survival benefit would be diluted and potentially even lost in the face of a small but real risk from complications from invasive procedures or radiation over years and years of scans that aren't demonstrated to improve survival in a younger or older population, or those with a minimal or no smoking history.

I see lung cancer screening as being woefully underutilized today despite the evidence to support it, and I believe this is because most primary care physicians and very possibly most insurers remain unconvinced that the benefit is really "worth it" for the cost of the intervention.  That's a shame, but diluting the benefit by screening a much lower risk population is not the way to improve the situation.  The evidence supports screening a population with a high enough risk of lung cancer...but screening more isn't necessarily better.