Lung cancer; although the term was formerly limited to malignant neoplasms arising from the epithelium of a bronchus or bronchiole, it is now applied generally to any primary malignancy of the lung or bronchial tract. Lung cancers are divided on the basis of predominant cell type into small cell carcinomas (15–25%) and non-small cell carcinomas (75–85%). Some tumors contain both cell types. Not included in this dichotomy are a small number (2–3%) of miscellaneous tumors (carcinoid, cylindroma, mucoepidermoid carcinoma). Small cell carcinomas of the lung tend to grow rapidly and metastasize early. They often produce hormones and antibodies capable of inducing paraneoplastic conditions such as hypercalcemia, Cushing syndrome, and myasthenia. Non-small cell carcinomas are subdivided into adenocarcinomas (50–60%; the most common type in women and nonsmokers), glandular cancers that usually arise peripherally, produce mucin, form tubular or papillary structures, and metastasize widely and early; squamous cell carcinomas (30–40%), which tend to develop centrally and in lower lobes and to metastasize more slowly; and the highly anaplastic large cell carcinomas (10%), which grow rapidly and produce carcinoembryonic antigen (CEA). Syn: non-small cell carcinoma.
Bronchogenic carcinoma is the leading cause of cancer deaths in the U.S. in both men and women, and the most common cancer in men world-wide. About 200,000 new cases of lung cancer are diagnosed each year in this country. The 5-year survival rate is 10–15%, depending on cell type. The increase in the incidence of lung cancer in the U.S. during the early 20th century closely followed the increase in cigarette sales, a fact first noted by Ochsner and DeBakey in 1941. A fall in the male:female ratio of lung cancer incidence began in 1935 and accelerated steadily with the increase in smoking among women. The age-adjusted death rate from lung cancer in women doubled between 1965 and 1974, and in 1987 bronchogenic carcinoma surpassed carcinoma of the breast as the most common fatal malignancy in women. Currently, about 90% of lung cancer deaths are directly attributable to cigarette smoking, and 25% of lung cancer in nonsmokers is due to involuntary (passive) smoking. About 11% of regular cigarette smokers develop lung cancer. Cancer risk is related to the age at which smoking began, the number of cigarettes smoked, and the depth of inhalation. Smoking cessation reduces the risk. Because adenocarcinoma of the lung is more common in families with other cancers and with inherited lung disorders, a genetic predisposition is probable. (Some people may also be genetically predisposed to nicotine addiction.) Inhalation of industrial carcinogens (particularly asbestos, silica, chromium, nickel, and polyvinyl chloride) and exposure to ionizing radiation or radon are other known causes. Bronchogenic carcinoma may encroach on the bronchial lumen or may invade adjacent lung parenchyma. The principal sites of metastasis are mediastinal lymph nodes, liver, brain, and bone. Complications include superior vena cava syndrome, esophageal obstruction, pericardial tamponade, phrenic nerve palsy, and Pancoast syndrome. Early symptoms (gradual onset of cough or change in a chronic cough, dyspnea, wheezing) may be wrongly attributed to smoking or to lower respiratory infection. By the time more ominous symptoms (hemoptysis, anorexia, weight loss, chest pain) occur, the condition is usually advanced and inoperable. Chest x-ray or computed tomography (CT) typically shows a solitary nodule and may also reveal evidence of atelectasis, pneumonic infiltrate, involvement of mediastinal nodes, or pleural effusion. MRI may detect invasion of vertebrae, spinal cord, or mediastinal structures. The diagnosis of carcinoma is confirmed by the finding of malignant cells in sputum, bronchial washings, or pleural fluid, or in biopsy material obtained by bronchoscopy, percutaneous needle aspiration, thoracoscopy, mediastinoscopy, or thoracotomy. Some studies suggest that screening high-risk populations (e.g., smokers aged 60 or older) by means of CT or sputum cytology reduces morbidity and mortality. Low-dose helical (spiral) CT is more sensitive than standard chest radiography in detecting lung cancer, but may not be cost effective even in high-risk populations. Surgical excision is the treatment of choice for bronchogenic carcinoma. Lung-sparing procedures (sleeve lobectomy, segmentectomy, wedge resection) may permit surgical excision in patients with limited pulmonary reserve but are associated with higher recurrence rates. Radiation therapy and chemotherapy with cisplatin, mitomycin, vinca alkaloids, ifosfamide, and etoposide are chiefly of use as palliative measures in advanced or inoperable disease.
Reference: Stedman's Medical Dictionary