Efficacy of CT screening for lung cancer in never-smokers: analysis of Japanese cases detected using a low-dose CT screen

Abstract

CT-screening for lung cancer is fairly widely used for both smokers and never-smokers in East Asia because the mortality rate for never-smokers due to this cancer is relatively high in this region. We performed comparative analyses, as a retrospective study, on three lung cancer arms detected by CT-screen, X-ray-screen, and via analysis of clinicopathological features and outcomes in never-smokers from a symptomatic-prompted group of patients. The total study cohort comprised 218 patients in CT group, 160 in X-ray group, and 82 in symptomatic-prompted group. The percentage of bronchioloalveolar carcinoma (BAC) was 65.1% in CT-screen group. The ratio of stage IA tumors in CT-screen group was 88.5% and the ratio of advanced cases (i.e. stages IIIB+IV) was 2.3%. The 5-year-survival rates were 95.0% in CT-screen, 73.0% in X-ray-screen and 40.0% in symptomatic-prompted group. We performed further sub-analysis which excluded pure BACs (i.e. Noguchi types A and B) or pure GGOs within a 10mm diameter because this is indicative of a very favorable prognosis. Based on this sub-analysis the number of the subjects in each group became 76 in CT group; 140 in X-ray group and 77 in symptomatic-prompted group. The principal characteristics of the patients such as age and sex became almost even in the three arms. In CT-screen subgroup, the ratio of stage IA cancer was 69.7% and of advanced cases was 6.6%. This advanced ratio was lower than both X-ray-screen (22.1%) and symptomatic-prompted (61.9%) groups. The 5-year-survival rates were 89.9% among CT-screen group patients, 72.6% for X-ray screen cases and 39.1% in symptomatic-prompted group. A CT-screen was found to be one of the independent prognostic factors for lung cancer (HR, 0.28; 95% CI, 0.12-0.72) and based on this would be expected to reduce the risk of lung cancer death by 78% compared with non-screened cases. In conclusion, CT will improve the survival rate and decrease the rate of advanced cancers in never-smokers via the existing annual screening system. CT-screening is also an independent prognostic improvement factor in never-smokers, and will therefore reduce the risk of lung cancer death.