Lung cancer causes over 120,000 deaths per year in the United States and is the leading cause of cancer deaths in men and women. Carcinoma of the lung is most common in the fifth and sixth decades and is rarely seen before the age of 35.
Cigarette smoking is the most important causative factor, with lung cancer being 10 to 30 times more common among smokers; approximately 4% of those who have smoked for 40 years develop lung cancer. While there is still some controversy, most experts feel that there is a small but significant risk to the development of lung cancer from environmental or passive ‘smoke exposure. All cell types except bronchoalveolar carcinoma are associated with smoking of the other causative agents, asbestos is the most important, especially when combined with cigarette smoking, and up to 14 per cent of smokers with asbestosis develop lung cancer. Other industrial risks include uranium, arsenic, chromium, chloromethyl, methylethers, polycylic aromatic hydrocarbons, nickel, and possibly beryllium. Lung cancer may rarely develop in pre-existing scars due to old granulomatous disease, diffuse interstitial fibrosis, or scleroderma.
Benign tumors, composing 5 per cent of the total, are usually diagnosed on routine chest x-rays, and symptoms, if present, are usually related to bronchial obstruction. The most common central tumor is the bronchial adenoma, which usually appears benign but is potentially malignant and rarely produces features of the carcinoid syndrome. The most common peripheral tumor is the pulmonary hamartoma, which has a characteristic “popcorn” pattern of calcification.
Primary malignant neoplasms of the lung can be classified on the basis of their cell type, as summarized in Table 1. The relative incidence of each cell type varies from study to study. Adenocarcinoma is the most common cell type (33% to 35%), followed by squamous cell (30% to 32%), small cell (20% to 25%), and large cell (15% to 20%). Bronchoalveolar carcinoma is considered a variant of adenocarcinoma. Squamous cell carcinoma spreads mainly by local invasion, whereas adenocarcinoma and large cell tumors metastasize early, especially to the central nervous system, skeleton, and adrenal glands. Small cell undifferentiated carcinoma, or oat cell carcinoma, has the greatest propensity to metastasize early in its course, leading most clinicians to assume disseminated-disease at diagnosis even without objective evidence.
Stafﬁng as a single malignant cell (10 µ size), 30 volume doublings are required to produce a tumor of 1 cm diameter, the smallest size detectable on a chest x-ray (Table 1). Ten further doublings produce a tumor 10 cm in diameter, but most patients die before the tumor reaches this size. Small cell carcinoma has the fastest doubling time and the worst prognosis. While adenocarcinoma has the longest doubling time, it has a worse prognosis than squamous cancers because of early extra thoracic spread.
Metastatic spread of neoplasms to the lung is common, involving the parenchyma, endobronchial mucosa, chest wall, pleural space, or mediastinurn. Direct extension is the least common mode of spread, occurring with breast, liver, and pancreatic tumors. Hematogenous spread is common with renal, thyroid, and testicular tumors and bone sarcomas and presents with asymptomatic discrete nodules on chest a-ray. Lymphangitic spread presents as an inﬁltrate or diffuse reticulonodular pattern on chest x-ray and causes severe dyspnea, usually out of proportion to the x-ray findings. This pattern is typical of spread from adenocarcinoma of the breast, stomach, pancreas, ovary, prostate, and lung.
Table 1. Features of malignant neoplasms
Clinical presentation may be related to tumor location within the chest, metastatic spread, or extra-pulmonary paraneoplastic manifestations. Most patients present with weight loss and symptoms related to local involvement such as cough (75%) that has changed in character, hemoptysis (50%) that is rarely life-threatening, dyspnea (60%), chest pain (40%), and a marked increase in sputum production with Broncho alveolar carcinoma. Pancoast’s syndrome refers to apical tumors that involve the brachial plexus and often lead to Homer’s syndrome resulting from invasion of the inferior cervical ganglion. Compression and obstruction of the superior vena cava, usually by small cell tumor, cause facial and upper extremity edema, dyspnea, stridor, and symptoms related to increased intracranial pressure. Partial obstruction of a bronchus may lead to unilateral, persistent wheezing, whereas complete obstruction causes post obstructive pneumonia. Recurrent laryngeal nerve involvement, typical of a left hilar mass, causes hoarseness.
Dr. Afsaneh Jeddi