A large-scale study of more than 150,000 individuals has confirmed that screening with chest radiography does not reduce death rates from lung cancer compared to no screening. The study, published in the October 26 issue of the Journal of the American Medical Association, might be most valuable for the insight it provides into CT lung screening.
Several previous studies in the 1970s and 1980s found no mortality benefit from radiography chest screening; as a result, such screening is neither commonly offered nor recommended in clinical guidelines in the U.S. These studies were relatively small and some had design flaws, however, which led to the design of the lung component of the Prostate, Lung, Colorectal, and Ovarian (PLCO) Cancer Screening Trial, according to lead author Dr. Martin Oken, of the University of Minnesota, and colleagues (JAMA, Vol. 306:16, pp. 1733-1818).
The PLCO trial began enrolling men and women ages 55 through 74 starting in 1993 and continuing through 2001 at 10 centers in the U.S. The lung component of the study did not require enrollees to be smokers, as the overall PLCO trial was screening for multiple cancers and not just lung cancer.
Individuals in the study's intervention group received a posterior-anterior chest radiography exam at baseline and then annually for three more years; participants who never smoked were not offered the third screening. Individuals in the control group did not receive any screening. Of a total of 154,901 participants, 77,445 were randomized to receive screening and 77,456 were randomized to the control group.
The study found only a slight reduction in mortality among the individuals who received screening, and the difference was not statistically significant. There were 1,213 lung cancer deaths in the screening group, compared with 1,230 in the usual-care group. This produced cumulative lung cancer mortality rates per 10,000 person-years of 14.0 in the screening group and 14.2 in the usual-care group, resulting in a rate ratio (RR) of 0.99 in terms of the ratio of deaths in the screening group versus deaths in the usual-care group (p = 0.48).
"These findings provide good evidence that there is not a substantial lung cancer mortality benefit from lung cancer screening with four annual chest radiographs," the authors wrote.
The authors then compared their results to those of the National Lung Screening Trial (NLST), which in 2010 found a 20% mortality benefit from low-dose CT screening of smokers. NLST compared CT screening to radiography screening, which raised the question of whether the benefits of CT screening would also hold true compared to a population of individuals who received no screening at all, similar to the control group in the PLCO trial.
Oken and colleagues pulled from the PLCO population a subset of individuals who met NLST's criteria in terms of smoking history and other factors. They found a mortality rate ratio of close to 1 (RR = 0.94) in comparing the populations, leading them to conclude that the 20% mortality benefit found for CT screening in NLST would probably also apply to individuals who never received screening.
