Lung-Cancer Mortality and Low-Dose CT Screening

Posted by Lisa Rosenbaum • August 3rd, 2011

A 65 year-old man comes to your office. Let’s call him Joe. He is former smoker, but quit 10 years ago after smoking one pack daily for 35 years. He has recently remarried, has two young children, and is worried about his risk for lung cancer. He saw on the news that CT scans are saving lives. He wants a CT scan.

What do you tell him?

Strictly speaking, he’s right: CT scans are saving lives. In a study published in this week’s NEJM, The National Lung Screening Trial Research Team report their findings on the efficacy of low-dose CT scans in reducing lung cancer mortality among high risk patients. Joe indeed is high-risk as defined by this study’s inclusion criteria: patients were between the age of 55 and 74, had to have at least a 30-pack year smoking history, and if former smokers, had quit within the last 15 years.

Over 50,000 patients who met these criteria were randomized and screened yearly by either CT or chest radiography for 3 years. They were then followed for 3.5 years with no screening. For the primary end point of lung cancer mortality, screening with low dose CT yielded a statistically significant reduction in lung cancer deaths, an absolute risk reduction of 20%. The authors estimate that there are 7 million such high-risk patients in the U.S., and an additional 94 million who are current or former smokers. Though 300 high-risk patients would need to be screened to prevent one death, these data suggest that one in five lung cancer deaths could be prevented.

Does this mean that we should be recommending screening for everyone who is at high risk? Not quite.

One potential harm associated with all screening tests is that of the false positive result. Indeed, of the positive results detected in this study, 96.4% in the low-dose CT group and 94.5% in the radiography group were false positives. Another issue that plagues any screening tool–be it a mammogram, a PSA, or a coronary calcium score–is the risk of overdiagnosis: that is, detection of a disease that would either regress on its own, or never become clinically consequential. The problem is that it is virtually impossible not to treat a disease once we find it, even though the toxicities of therapy may ultimately be more harmful than the tumor itself.

Given these potential harms of population-wide screening, these authors urge caution before translating these data into clinical practice. We still don’t know what these data mean for the 94 million at lower risk, nor how frequently or for how long the high-risk cohort should be screened. And above all, we don’t know if this is a cost-effective strategy, especially when compared to possible alternatives, such as smoking-cessation.

Wearing our health policy caps, it is clear these data are promising, but that CT screening is not ready for widespread implementation. But most of us wear a different cap, the one we wear daily when we enter the room of a patient eagerly awaiting our arrival who wants nothing more than to live to see his children grow up. How do you reconcile the needs and desires of Joe with the conclusion that CT screening may not be beneficial for society at large?

If you think it’s tough, you are not alone. In a series of experiments published in these pages twenty-one years ago, Drs. Donald Redelmeir and Amos Tversky described this very tension. They found that physicians make different recommendations for an individual patient than they would for a group composed of similar individuals. Using questionnaires describing clinical scenarios in which “reasonable” physicians might disagree, the authors randomized physicians to make decisions from either the individual, or the group standpoint. When it comes to the individual, physicians are more likely to recommend an additional test with a low cost and a possible benefit. They conclude, “Our findings are consistent with the notion that physicians give more weight to the personal concerns of patients when considering them as individuals and more weight to general criteria of effectiveness when considering them as a group.”

So what do you tell Joe? A CT scan is just a click away.

3 Responses to “Lung-Cancer Mortality and Low-Dose CT Screening”

  1. One of the best descriptions I’ve read of the difficult position PCPs are in when it comes to making smart decisions about diagnostic imaging and avoiding overutilization. Bravo!

  2. Dr Jessica Bowen says:

    Very practical approach to this common clinical dilemma. What should also be taken into account is the level of risk associated with exposure to such screening programmes in terms of radiation.

  3. prantesh jain says:

    it was not a absolute risk reduction ARR of 20 % but relative risk reduction ( RRR) which is 20 %. ARR was 0.33 %