Screening for Lung Cancer with Low-dose CT
The United States Preventive Services Task Force (USPSTF) gave a level B recommendation in support of annual low dose computed tomography (LDCT) to screen for lung cancer in appropriate risk groups. The USPSTF decision was largely based on the National Lung Screening Trial (NLST), a mega-trial (n = 53, 454) in the United States that randomized subjects to annual LDCT or chest X-ray. The primary endpoint of the study was lung cancer mortality; all-cause mortality was a secondary endpoint. Inclusion criteria included at least a 30-pack/year history of smoking (if cessated, within 15 years), ability and willingness to complete follow-up for abnormal findings, and absence of problematic comorbidities that might otherwise compromise long-term survival.
The good news is that LDCT was associated with a 20% relative risk reduction in lung cancer mortality, and a 7% reduction in all-cause mortality, both of which were statistically significant. Should we end the discussion there?
Perhaps not. The NLST has several stark limitations. First, literally 95% of “positive” findings on LDCT were false-positive, and harm to patients during the follow-up evaluations were substantial, including death. Second, a not-inconsiderable number of “incidentalomas” were also detected, and follow-up data on whether things findings favorably (or unfavorably) affected study subjects’ lives have not yet been published.
Finally, an issue about the absolute magnitude of benefit: Although the 20% relative reduction in lung cancer mortality sounds impressive, the absolute risk reduction was very small; In the LDCT group, 356 of 26,309 died (1.3%) vs. 443 of 26,035 in the chest X-ray group (1.7%), for an absolute risk reduction of 0.348%.
Although most major organizations have endorsed USPSTF recommendations, the American Academy of Family Physicians (AAFP) has issued a note of caution, based upon lack of replication of these data in a community setting. Instead of universal screening, they suggest a “shared decision-making” approach reminiscent of their advice about prostate cancer screening in the recent past.
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