Efficacy of lung cancer screening: a case-control study in atomic bomb survivors

INTRODUCTION:  While the randomized trial of the Prostate, Lung, Colorectal, and Ovarian (PLCO) cancer screening trial in United States suggested that annual lung cancer screening would not decrease lung cancer mortality, case-control studies conducted in several regions of Japan indicated the efficacy of annual screening. We conducted a case-control study in the atomic bomb survivor cohort to reduce the self-selection bias.

METHODS: A total of 448 lung cancer deaths were observed in the cohort members who were in Nagasaki city during the observation period, i.e. from 1 Jan. 1989 to 31 Dec. 2007, who had opportunities to undergo screenings during the period and who were alive as of 1 Jan. 2000. Excluding 209 subjects whose age at death was 80 years or over and who had no information on smoking status, 239 subjects were identified as cases. For each case an attempt was made to select 3 controls matched by sex, year of birth, smoking status and radiation exposure status, and 713 subjects were selected as controls. The odds ratios and 95% confidence intervals (CI) of death for screened individuals versus unscreened before diagnosis of lung cancer were calculated by the conditional logistic regression analyses with adjustment by smoking index using PROC PHREG of the SAS^©.

RESULTS: The proportions of those screened within 12 months before diagnosis were 12.6 % and 23.6 % in cases and controls, respectively. Adjusted odds ratio was 0.56 (95% CI: 0.35-0.88, P=0.012). The lung cancer mortality was significantly lower in screened individuals than those unscreened. Furthermore, the proportions of screened almost every year were 6.3 % and 12.3 % in case and control, respectively. Adjusted odds ratio was 0.52 (95% CI: 0.27-1.00, P=0.050).

CONCLUSIONS: The present case-control study in the Nagasaki atomic bomb survivors cohort indicated reduction of lung cancer mortality by 44% by annual lung cancer screening.