Category VI: Malignant

A high percentage of cytologic specimens obtained from pulmonary nodules, masses, and cystic lesions are malignant. Indeed the majority of cytologic studies of material obtained from the lower respiratory tract are performed for the investigation as to whether or not a pulmonary lesion is malignant. The lungs are the site of a large number of primary and metastatic malignancies as well as a smaller number of benign neoplasms and localized nonneoplastic conditions. Cytologic recognition of an imaging finding as definitively malignant is extraordinarily important for development of a therapeutic plan. Given today’s therapeutic requirements, a number of specific questions must be answered including (1) whether a lesion is malignant or benign, (2) whether the lesion represents a primary carcinoma or some other lesion, (3) whether the carcinoma is small cell or non-small cell in type, and (4) whether a non-small cell carcinoma is an adenocarcinoma or a squamous cell carcinoma. A number of molecular and immunohistochemical studies are often required for the proper characterization of primary pulmonary carcinomas. The malignancy risk for the malignant category is approximately 90%.