Lung Cancer Screening (PDQ®): Screening - Health Professional Information [NCI] - Description of the Evidence
The design of the Mayo Clinic study (known as the Mayo Lung Project, or MLP), was different. All potential participants were screened with chest imaging and sputum cytology, and those known or suspected to have lung cancer, as well as those in poor health, were excluded. Remaining persons were randomly assigned to either an intervention arm that received chest imaging and sputum cytology every 4 months for 6 years, or to a control arm that received a one-time recommendation at trial entry to receive the same tests on an annual basis. No reduction in lung cancer mortality was observed. The MLP was interpreted in the 1970s as showing no benefit of an intense screening regimen with chest x-ray and sputum cytology. The Czechoslovakian study began with a prevalence screen (chest imaging and sputum cytology) of 6,364 males aged 40 to 64 years who were current smokers with a lifetime consumption of at least 150,000 cigarettes.[49,50] All participants except the 18 diagnosed with lung cancer as a result of the prevalence screen were randomly assigned to one of two arms: an intervention arm, which received semi-annual screening for 3 years, or a control arm, which received screening during the third year only. The investigators reported 19 lung cancer deaths in the intervention arm and 13 in the control arm, and concluded that frequent screening was not necessary.
At the end of the 1980s, the relationship between screening with chest imaging (using traditional chest x-ray) and lung cancer mortality was not well understood. Although previous studies showed no benefit, they were not definitive, partly due to lack of statistical power. A multiphasic trial with ample statistical power, the Prostate, Lung, Colorectal and Ovarian (PLCO) Cancer Screening Trial, began in 1992. PLCO enrolled 154,901 participants aged 55 to 74 years, including women (50%) and never smokers (45%). Half were randomly assigned to screening, and the other half were advised to receive their usual medical care. PLCO had 90% power to detect a 20% reduction in lung cancer mortality.
The lung component of PLCO addressed the question of whether annual single-view (posterior-anterior) chest x-ray was capable of reducing lung cancer mortality as compared with usual medical care. When the study began, all participants randomly assigned to screening were invited to receive a baseline and three annual chest x-ray screens, although the protocol ultimately was changed to screen never-smokers only three times. At 13 years of follow-up, 1,213 lung cancer deaths were observed in the intervention group, compared with 1,230 lung cancer deaths in the usual-care group (mortality relative risk, 0.99; 95% CI, 0.87–1.22). Sub-analyses suggested no differential effect by sex or smoking status.