Previous lung cancer screening trials in the United States (US) employing chest X ray and sputum cytology did not demonstrate reductions in lung cancer mortality. However, recent case control studies in Japan demonstrated a decrease in lung cancer mortality in the computed tomography (CT) screened group. Lung cancer screening using chest CT detected more cancers at an earlier stage than chest X ray. Before CT screening is widely performed, lung cancer mortality reduction should be proved in a scientific manner. The problem of a much higher false positive rate of this method should be solved. The subtypes of adenocarcinoma; bronchioloalveolar carcinoma (BAC) tends to show specific CT findings called ground glass opacity (GGO) and a favorable prognosis can be expected. BAC is usually invisible by chest X ray and detected only by CT. Recent studies have shown the proportion of GGO is strongly related to biological malignancy of small adenocarcinoma. Based on this fact, thoracic surgeons wish to identify the possibility of limited resection for minimally invasive cancers. Lung cancer researchers are interested in evaluating the nature of small adenocarcinoma as well as the carcinogenic process. A comprehensive understanding of screening-detected cancers including the CT images, pathology and genetic analysis is necessary for optimum management of such nodules.