Description of the Evidence
Evidence of benefit associated with screening
Screening by low-dose helical computed tomography
There have been intensive efforts to improve lung cancer screening with newer technologies, including low-dose helical computed tomography (LDCT) and molecular techniques.[12,13] LDCT was shown to be more sensitive than chest radiography. In the Early Lung Cancer Action Project (ELCAP), LDCT detected almost six times as many stage I lung cancers as chest radiography, and most of these tumors were no larger than 1 cm in diameter. The ability of LDCT to reduce lung cancer mortality was demonstrated in the randomized, controlled National Lung Screening Trial (NLST): a statistically significant relative reduction of 20% in lung cancer mortality was observed, as was a statistically significant 6.7% relative reduction in all-cause mortality.
Eight observational studies of LDCT in various parts of the world have been reported and summarized. These are relatively small studies, ranging from about 600 to 8,000 participants, which began between 1992 and 2000. Most of the studies include a substantial percentage of females, and the studies in Japan include nonsmokers. Findings include a nodule or positivity rate of 5% to 51%, 0.4% to 3% lung cancers, 50% to 95% adenocarcinomas, 50% to 91% stage I or IA cancers, and estimates of sensitivity ranging from 40% to 95%.
False-positive test results and overdiagnosis must be considered when lung cancer screening with LDCT is being evaluated. The false-positive test result, which is more common than overdiagnosis, may lead to anxiety and invasive diagnostic procedures such as percutaneous needle biopsy or thoracotomy. In the ELCAP study, which used a CT slice thickness of 10 mm, noncalcified nodules were detected in 21% of patients without lung cancer at the prevalence screen. Thirty-one (13%) of 233 individuals with noncalcified nodules underwent biopsies, of which close to 90% (27 of 31 patients) resulted in a diagnosis of malignancy, and the prevalence of cancers detected was 2.7%.
In a case series that defined the population at high risk of lung cancer by occupations associated with asbestos exposure, 58% accepted an invitation to participate in an LDCT screening program. The ELCAP screening protocol was applied in 1,119 asbestos-exposed people whose average age was 57 years. Twenty-five biopsies resulted in the detection of one stage IA and four late stage lung cancers. The authors concluded the screening program was not able to replicate the ELCAP results and was not cost effective for lung cancer screening in this population.