Jan 262014

It's official: the U.S. Preventive Services Task Force (USPSTF) announced its formal recommendation for yearly low-dose chest CT screening for lung cancer in high-risk individuals on December 30, 2013.

The final grade B recommendation (“Suggestion: offer or provide this service”) was virtually unchanged from the draft recommendations the USPSTF made in July 2013. It advises adults 55 to 79 years old with at least a 30 pack-year history of smoking who have quit for less than 15 years to get annual chest CTs for up to 26 years. Those with significant illnesses limiting life expectancy, or who would not be able to undergo curative surgery, should not be screened, the panel advised.

By making lung cancer screening the standard of care for the 9 million eligible Americans, the final recommendation by the USPSTF will have far ranging effects on physicians in primary care, pulmonary and radiology.

Since the publication of the National Lung Screening Trial in 2011, lung cancer screening programs have rapidly proliferated across the U.S., as medical centers compete for the leading-edge, and also for potentially lucrative patients. Otis Brawley of the American Cancer Society estimated that each of the 95% false positive lung cancer screening CTs would cost about $45,000 (or generate $45,000 in revenue, depending on your point of view).

The new grade B recommendation should markedly accelerate the trend, since the Affordable Care Act requires private insurers to cover services the task force grants an "A" or a "B" recommendation without copay or deductible – in other words, free. Medicare will not be required by law to cover lung cancer screening (but could still decide to). Since primary care and other physicians will be responsible for missed lung cancer diagnoses if they do not offer screening, low dose CT screening should soon achieve “reflex” status, like mammography and colon cancer screening.

That could save up to 12,000 lives yearly from the #1 cancer killer in the U.S. (201,144 diagnoses, 158,248 deaths in 2010), for which medical treatments have been poorly effective. But industrial-scale screening of 9 million qualifying patients will also come with some growing pains: overdiagnosis of harmless lung cancers and new professional demands on primary care physicians, pulmonologists, radiologists, and thoracic surgeons.

The reasons can be summed up in a simple phrase: false positives. About 35% of patients in the NLST had at least one false positive scan in 3 years, requiring further follow-up CTs and occasionally, biopsy or surgery, for lesions that were not cancer. Since 95% of all the nodules and other lesions seen were false positives, nationwide screening can be expected to generate a massive new data feed of hundreds of thousands of new CT scans and follow-ups, which most centers’ systems are not currently prepared to handle. Screening people for as long as 26 years should be expected to produce even more false positive CT scans per patient than seen in the NLST.

The lower the risk in the group of patients tested, the higher the false positive rate will be. Although adults in the NLST all had a heavy smoking history, that similarity masked important differences between them that resulted in a dramatic variation in risk, and in the rate of false positive scans.

Among the highest-risk cohort in the NLST, the number needed to screen to prevent a death from lung cancer was only 161, but in the lowest-risk cohort (all of whom still had 30 pack year histories, remember), 5,276 people needed to be screened to save a life. The 20% of heavy smokers in the lowest-risk category had a 99.98% chance of having no benefit from screening. This is partly why lung cancer screening only got a grade B recommendation, with "moderate certainty of a moderate net benefit."

Is there radiation risk from lung cancer screening? Low-dose chest CT delivers about 2 mSv (each year); atomic bomb survivors’ mean dose was 40 mSv. The risk of getting cancer from a 1-10 mSv radiation dose has been estimated to be 1 in 10,000. Most estimates conservatively assume the risk from serial CT scans is additive (so 20 years of CT scanning = one atomic bomb exposure), however, cellular DNA repair between low-dose scans may mitigate this risk.

Researchers are working on prospectively validating lung cancer risk calculators (the ones that produced some of the above data) to better stratify the risk of patients with heavy smoking histories. Deployed systematically, these would allow the most rational and productive use of lung cancer screening CT, saving lives while reducing harm to cancer-free patients. You can play with the not-ready-for-production tools yourself.

As the headlines dissolve into workaday health care policy, practical implementation of lung cancer screening will fall to physicians and the systems we work in. There was no standardized follow-up protocol for abnormal lung scans in the NLST, so to some extent, this is an open field. Many primary care physicians, radiologists and pulmonologists will try to just add this new item to the long list of stuff they already need to do. My suspicion is the frequency and volume of follow-up CTs needed for the deluge of false-positive tests will quickly become unmanageable using such an ad hoc approach. Referral to medical centers with established lung cancer screening programs, potentially with remote/telemedicine consultations for underserved areas, may be more likely to approach the 20% mortality reduction in the NLST.

Lung cancer screening with low dose chest CT is a crude but effective tool that should evolve and improve over time. In large part, that evolution will be determined by physicians implementing the recommendation. So what are you waiting for -- fire up those scanners, print out those Fleischner guidelines, and start saving some lives. (Every 320 scans, you can score yourself one.)

USPSTF website, "Screening for Lung Cancer: Current Recommendation," December 2013.

Frank C. Detterbeck and Michael Unger.  Screening for Lung Cancer: Moving Into a New EraAnn Intern Med. Published online 31 December 2013.

Bach PB. Raising the Bar for the U.S. Preventive Services Task Force. Ann Intern Med 2013 Dec 31. doi: 10.7326/M13-2926.

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US Gov’t pronounces lung cancer screening the standard of care