Book 4 - Self Instructional Manual for Cancer Registrars - SEER ...

Malignant TumorsCarcinoma of the lung originates in the mucosal lining of the bronchi, bronchioles, and alveoli.The tumors may grow into the lumen of the bronchus or they may invade the wall of the bronchusinto the lung parenchyma. Most bronchogenic carcinomas arise near the hilus of the lung and willextend along the main bronchus towards the carina into the mediastinum involving the organs andstructures located in the mediastinum--the pericardium, major blood vessels and nerves, trachea, andesophagus--or they may extend peripherally to invade the pleura, chest wall, and ribs.The histologic types of neoplasms which are commonly found in the lung are listed below:• Squamous cell carcinoma is the most common type of bronchogenic carcinoma. It isbelieved to arise as a result of irritation of the bronchial mucosa causing squamousmetaplasia progressing to squamous cell carcinoma. Cigarette smoking has been linked tothe increasing incidence of squamous cell carcinoma of the lung.• Adenocarcinoma may arise from the mucous glands embedded in the submucosa, or, sinceboth adenocarcinoma and squamous cell carcinoma arise in the bronchus, it is thought thatall bronchogenic carcinomas may arise from the multipotential reserve cells I of thebronchial epithelium. Adenocarcinomas tend to occur more peripherally than do squamouscell carcinomas.• Adenosquamous carcinoma (adenoacanthoma) is a tumor of mixed histologic type.• Undifferentiated carcinoma, which is indistinguishable as either squamous cell carcinomaor adenocarcinoma, probably arises from the reserve cells. It may occur, for example, aslarge cell, small cell, or oat cell variants. These carcinomas have a worse prognosis thanany of the above.• Bronchiolar (alveolar) carcinoma arises in the terminal bronchioles or alveoli and is a raretumor type.• Bronchial adenoma is somewhat of a misnomer for a tumor that is frequently invasive.Variants are the carcinoid or cylindroid which are invariably malignant.• Mesothelioma arises in the pleura or mesothelium that lines the pleural cavities and coversthe lungs. It may be either benign or malignant.• Carcinoids arise from enterochromaffia (EC) cells which occur primarily in the submucosaof the main bronchi.The lung is one of the most common sites of metastatic disease since the body's blood flowsdirectly into this organ and all lymphatic drainage, whether direct or retrograde, eventually flows intothe lungs.1reserve cells--Cells of the basal or germinal layer of the bronchial epithelium.157