Definition
Bronchogenic carcinoma is a malignant neoplasm of the lung arising from the epithelium of the bronchus or bronchiole.

Pathology
Bronchogenic carcinomas begin as a small focus of atypical epithelial cells within the bronchial mucosa. As the lesion progresses, the atypia becomes frankly malignant and the neoplasm grows in size. The neoplasm may grow into the bronchial lumen, along the mucosa or into the bronchial wall and adjacent lung parenchyma. Eventually the neoplasm spreads to regional lymph nodes and distant organs such as the liver, brain and bone. Most bronchogenic carcinomas form a mass in or near the hilus. Some neoplasms, especially the adenocarcinomas, form a mass in the periphery of the lung. Refer to Figure 15-42 in your textbook. The following classification scheme represents the major histologic types of bronchogenic carcinoma. Refer to Table 15-10 in your textbook.

• Squamous Cell Carcinoma: The neoplasm is composed of malignant squamous cells which may vary in degree of differentiation from tumor to tumor. A well differentiated squamous cell carcinoma may form keratin and intercellular bridges. Refer to Figure 15- 44 in your textbook. CLINICAL NOTE: This neoplasm is most common in men and is closely related to smoking.
• Adenocarcinoma: The neoplasm is composed of malignant glandular epithelium which may vary in degree of differentiation from tumor to tumor. Well differentiated neoplasms may form distinct glands, other neoplasms may vary from forming papillary structures to solid neoplasms without any gland formation. Adenocarcinomas tend to be smaller than other bronchogenic carcinomas and located in the periphery of the lung. A distinctive type of adenocarcinoma is bronchioloalveolar carcinoma. CLINICAL NOTE: This neoplasm is the most common type in women and nonsmokers.
• Small cell carcinoma: The neoplasm is composed of small cells containing dark blue, round nuclei and sparse cytoplasm. These cells resemble (but are not) lymphocytes and are arranged in clusters. Refer to Figure 15-43 in your textbook. Electron microscopy reveals that these cells contain neurosecretory granules, indicating their origin from neuroendocrine cells. Refer to Figure 15-44 in your textbook. CLINICAL NOTE: This neoplasm is strongly related to smoking. It is a very aggressive neoplasm, generally having metastasized at the time of diagnosis.
• Large cell carcinoma: The neoplasm is composed of large, undifferentiated malignant cells.
• Bronchioloalveolar carcinoma: The neoplasm is a distinctive form of adenocarcinoma. The neoplasm arises from the epithelium of the terminal bronchiole or the alveolus. The neoplastic cells are columnar, lining alveoli or form palliary growths which project into the alveolus. Refer to Figure 15-45 in your textbook. The neoplasm, almost always arising in the periphery, is solitary or forms multiple coalescing nodules.

Pathophysiology

• Bronchogenic carcinoma tends to form an intraluminal mass which may partially or completely obstruct the bronchus. The neoplasm also may compress or invade local structures such as aorta, esophagus, superior vena cava or cervical sympathetic chain. What are the clinicopathologic consequences of obstruction or invasion?
• Bronchogenic carcinoma may present with a variety clinical manifestations but the major findings are cough, weight loss, chest pain and dyspnea. These neoplasms also have the capacity to secrete hormones or hormone-like substances which have a variety of clinical effects.