At this point the pulmonary morphologic changes are considered to be irreversible. Lung Cancer Lung cancer is divided into subtypes based on the differentiation of cells within the neoplasm. In squamous cell carcinoma there is often keratin pearl formation along with intercellular bridges. This tumor occurs in larger, more centrally located bronchi. Adenocarcinomas are usually composed of malignant glandular or papillary elements, often with mucin production.
Adenocarcinomas tend to be more peripherally located.
A distinctive subtype of adenocarcinoma, bronchoalveolar cell carcinoma , is characterized by growth of malignant cells along the preexisting alveolar framework. These tumors may present as a single nodule, multiple nodules, or in a pattern which looks like a pneumonic process. Large cell carcinoma consists of sheets of poorly differentiated malignant cells without glandular or squamous differentiation. Small cell carcinomas are distinct from the others. They consist of small cells with very little cytoplasm growing in clusters or cords without squamous or glandular differentiation.