Low-dose CT Detects Twice as Many Early-stage Lung Cancers as Chest X-ray, According to Additional NLST Results

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Today’s publication represents the type of immensely important data NLST will continue to provide about lung cancer screening in the United States.

—Mitchell D. Schnall, MD, PhD

Results of the first of three planned annual screening examinations from the National Lung Screening Trial (NLST) were recently published and physicians may now have more information to share with their patients about the benefits and risks of low-dose computed tomography lung cancer screening.1

“For a cancer screening to work, it’s important to verify that it can in fact discover cancers early. The analysis of NLST participants’ initial annual screening examination provides evidence that the number of early-stage cancers detected in the trial’s CT arm were significantly greater than the number detected in the chest x-ray arm,” said Timothy Church, PhD, a biostatistician and Professor in the School of Public Health at the University of Minnesota who has been involved with the NLST’s design, implementation, and analysis.

Dr. Church also pointed out that a reduction in mortality is the ultimate indicator of a successful cancer screening strategy.

The NLST is a large-scale, longitudinal clinical trial that randomly assigned over 53,400 study participants equally into either the low-dose CT or standard chest x-ray arm to evaluate whether lung cancer screening saves lives. Published results reported a 20% reduction in lung cancer deaths among study participants (all at high risk for the disease) screened with low-dose CT vs those screened with chest x-ray.2

Initial Screening Results

The authors reported that the NLST initial-screening results are reflective of other large trials with regard to positive low-dose CT vs chest x-ray results, with more positive screening exams (7,191 vs 2,387, respectively), more diagnostic procedures (6,369 vs 2,176, respectively), more biopsies and other invasive procedures (297 vs 121, respectively), and more lung cancers seen in the low-dose CT arm than in the chest x-ray arm during the first screening round of NLST (292 vs 190, respectively).

Need for Follow-up Small

Although these results were generally anticipated, a key reason to publish the data was to document the exact differences between the two arms. “Although we did see that CT resulted in referring more patients for additional testing, the question comes down to whether the 20% reduction in mortality is worth the additional morbidity introduced by screening high-risk patients,” said Dr. Church. He noted that although there were more follow-up procedures in the low-dose CT arm vs the chest x-ray arm, it was encouraging to confirm that the number of individuals who actually had a more invasive follow-up procedure was quite small.

High Rate of Compliance

Another result reported is the high rate of compliance in performing the low-dose CT examination as specified in the research protocol across the 33 imaging facilities that carried out the study. “The sites complied with the low-dose CT imaging protocol specifications in 98.5% of all studies performed, which is outstanding considering the many thousands of scans performed,” stated Denise R. Aberle, MD, the national principal investigator for NLST-ACRIN and site co-principal investigator for the UCLA NLST team.

Dr. Aberle, a member of the UCLA Jonsson Comprehensive Cancer Center, Professor of Radiology and Bioengineering and Vice Chair for Research in Radiology at UCLA, also emphasized that the first-screen result strongly suggests that CT lung cancer screening programs with radiologists who possess similar expertise and interpret similar numbers of CT cases that are obtained on scanners of the same caliber or better as those required for the NLST are likely to have results similar to those reported in the paper.

Valuable Results

“What we’ve learned from the analysis of the first-screen results provides clinicians additional facts to discuss with patients who share similar characteristics as the NLST participants (current or former heavy smokers over the age of 55),” said Dr. Church. “The results also caution against making blanket lung cancer screening recommendations, because each person’s trade-off between the risk of having an unnecessary procedure and the fear of dying of lung cancer is uniquely individual.”

“Today’s publication represents the type of immensely important data NLST will continue to provide about lung cancer screening in the United States,” said Mitchell D. Schnall, MD, PhD, ACRIN Network Chair, group Co-Chair of the ECOG-ACRIN Cancer Research Group and Chair of the Radiology Department of the University of Pennsylvania. ■

Disclosure: The NLST was supported by the National Cancer Institute through the grants U01 CA079778 and U01 CA080098.


1. The National Lung Screening Trial Research Team: Results of initial low-dose computed tomographic screening for lung cancer. N Engl J Med 368:1980-1991, 2013.

2. The National Lung Screening Trial Research Team: Reduced lung-cancer mortality with low-dose ccomputed tomographic screening. N Engl J Med 365:395-409, 2011.

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SIDEBAR: Low-dose CT Screening

The first-screening results strongly suggest that the 20% reduction in lung cancer mortality with low-dose CT vs x-ray reported in the original NLST paper is achievable at experienced screening centers.