Results of annual screening of lung cancer with low dose computed tomography in 5,000 high-risk individuals

Background: Screening detected lung cancers are correlated with good prognosis however most of the reported cases were detected at baseline screening and little is known about the evolution of pulmonary nodules at annual screening. We report the results of the first and second year of a single centre screening trial focusing the attention on the evolution of pulmonary nodules. Methods: The Cosmos trial started in October 2004 and enrolled 5,202 asymptomatic persons at high risk for lung cancer in one year. Between October 2005 and October 2006, the participants of the study, have been recalled to undergo the annual low dose CT. New lesions were treated according to the baseline diagnostic work up protocol. Previously detected lesions grown at annual screening were investigated with repeated low dose CT and/or Pet scan. Surgical biopsy was scheduled in case of Pet positive or growing nodules. Stable lesions were sent to one year follow up. Results: 4,745 out of 5,202 underwent the annual screening (compliance 92%). Recall rate was 10.7% at baseline and 4% at annual screening. Rate of malignant disease was 1.03% at baseline and 0.7% at annual screening. Patients with stage I disease were 68% at baseline and 76% at annual screening. Of the 32 lung cancers diagnosed at annual screening 8 were new nodules, 1 nodules was stable and 23 nodules progressed from the previous year. Among these, 9 nodules were lower than 5 mm at baseline (out of 2,190 subjects = 0.4%) and 14 were larger than 5 mm (out of 560 subjects =2.5%). Conclusions: Screening low dose spiral CT is an effective tool for the early detection of lung cancer. At first annual screening malignancy rate decreased from 1% to 0.7% and stage distribution was more favourable. However the high rate of delayed diagnosis (2.5%) in cases of nodules larger than 5 mm at baseline CT may require a revision of our proposed diagnostic work up protocol to further anticipate detection of these cases.