Screening X-rays don't reduce lung cancer mortality

Annual screening with chest radiographs over a four-year period did not reduce lung cancer mortality compared with usual care, according to researchers analyzing results of the Prostate, Lung, Colorectal, and Ovarian (PLCO) Cancer Screening Trial.

The PLCO trial is a randomized, controlled trial of 154,901 smokers and nonsmokers 55 through 74 years of age. Of this group, 77,445 were assigned to annual screenings and 77,456 were assigned to usual care between November 1993 and July 2001. Results appeared online Oct. 26 in the Journal of the American Medical Association.

Participants randomized to the intervention group were offered a posterior-anterior chest radiograph at baseline and then annually for three more years. If a nodule, mass, infiltrate, or other abnormality considered suspicious for lung cancer was noted, patients were advised to seek diagnostic evaluation from their own physicians. PLCO screening center staff obtained medical records related to diagnostic follow-up.

Participants in the usual care group were offered no interventions and received their usual medical care. All diagnosed cancer, deaths, and causes of death were ascertained through 13 years of follow-up or until Dec. 31, 2009.

Cumulative lung cancer incidence rates through 13 years of follow-up were 20.1 per 10,000 person-years in the intervention group and 19.2 per 10,000 person-years in the usual care group (rate ratio [RR]; 1.05, 95% CI, 0.98 to 1.12). Although incidence rates were dependent on smoking history (3.1 for never smokers, 23 for former smokers, 83 for current smokers), the RRs for incidence were similar according to smoking history: 1.06 for never smokers, 1.12 for former smokers, and 1.00 for current smokers. A total of 1,213 lung cancer deaths were observed in the intervention group compared with 1,230 in usual care group through 13 years (mortality RR, 0.99; 95% CI, 0.87 to 1.22). Researchers concluded that annual chest radiographic screening for up to four years did not have an effect on cumulative lung cancer mortality during 13 years of follow-up.

The PLCO data were then analyzed in an ancillary analysis with another trial, the National Lung Screening Trial (NLST), which compared chest radiographs with spiral computed tomography (CT) screening. The authors noted that because the NLST did not have a usual care group, examining its findings alongside the PLCO study was critical to addressing the benefit and harms of CT compared with usual care.

The findings from the NLST, which demonstrated a 20% mortality benefit (RR, 0.80) for screening with low-dose spiral CT compared with chest radiograph, were compared with the findings for chest radiograph versus usual care for the PLCO subgroup that would have been eligible for NLST. Through the approximate six-year period, the mortality RR in the NLST-eligible PLCO cohort was 0.94 (95% CI, 0.81 to 1.10). The study authors wrote, “Although there were some modest differences between the 2 cohorts, it seems reasonable to consider the chest radiograph vs usual care comparison in the NLST-eligible cohort in PLCO to be an adequate surrogate for such a comparison within NLST.”

An accompanying editorialist commented that the results of the PLCO lung cancer study convincingly indicate that using chest radiography to screen for lung cancer is not effective. “The study is important for putting this question to rest and providing strong empirical grounds for comparing low-dose CT to a real-world alternative: usual care,” the editorialist wrote.