The cytologic basis for classification of lung tumors.

Nuclear changes in cells of bronchial biopsies and surgical specimens were studied in relation to nuclear structures of cells at various mitotic phases. Cell structures comparable to early and late G1 and G2 phases were correlated with histologic types of lung tumors according to the 1981 WHO classification. The evolved cellular classification added another parameter for diagnosis of histologic alterations and for interpretation of cellular changes in cytologic specimens. Benign histological alterations contained cells in either early or late G1 phase. Well-differentiated adenocarcinomas, bronchiolo-alveolar cell carcinomas, and carcinoid tumors had cells with structure of the late G1 phase. These were distinguished from benign cells with similar structures by their increased nuclear size, their increased amount of nuclear chromatin, hyperchromasia, and increased nuclear cytoplasmic ratio. Well-differentiated acinar adenocarcinomas, papillary adenocarcinomas, clear cell carcinomas, and large cell carcinomas had cribriform nuclear structures with prominent nucleoli related to early G2 phase. Squamous cell carcinomas, poorly differentiated adenocarcinomas, giant cell carcinomas, and solid carcinomas with mucus formation had usually prominent nucleoli with nuclear structures of the late G2 phase. Small cell carcinomas were the only malignant tumors of the lung that had cells with the malignant cribriform nuclear structure of the early G2 phase without a nucleolus. Cellular markers of malignant neoplasms had also the nuclear structure of early G2 without a nucleolus but differed from small cell carcinoma by their differentiated state with presence of cilia. The cytologic diagnosis of 506 malignant tumors of 1031 cases examined resulted in a sensitivity of 86.6%. The correct diagnosis of 244 of 247 cases without tumor resulted in a diagnostic specificity of 98.8%.