Small peripheral glandular lesions detected by screening CT for lung cancer. A diagnostic dilemma for the pathologist.

The early detection of lung cancer by helical CT provides an important opportunity for radiologic-pathologic and clinical correlation of borderline glandular lesions. Little is known about the clinical course of atypical adenomatous hyperplasia, solitary noninvasive, nonmucinous BAC, and early-phase invasive adenocarcinomas, therefore, a single protocol for specimen handling and a central tissue registry are essential. The most important separation among the various types of adenocarcinoma is the diagnosis of BAC, a potentially curable malignancy, from invasive adenocarcinoma. Therefore, for small lesions of 2 cm or less, the entire tumor should be processed. For larger lesions, one section per centimeter should be sampled, and if the initial sections show a purely lepidic growth pattern, additional sections should be taken to exclude an invasive component. If foci of invasion are identified, the tumor should be classified as an adenocarcinoma with bronchioloalveolar features. At the International Conference on Screening for Lung Cancer held in October 1997, it was recommended that an international panel be used to reach consensus on difficult lesions of the lung detected by CT screening, and that a tissue bank of these lesions be established to ensure further clinical, radiographic, light microscopic, immunohistochemical, and molecular studies of putative precursor lesions and small carcinomas. Through the collection of these lesions, we can further our understanding of the biologic behavior of lung cancer, particularly because little is known about the progression from a purely lepidic growth pattern to invasive adenocarcinoma.