Lung cancer usually develops within the wall or epithelium of the bronchial tree. Its most common types are epidermoid (squamous cell) carcinoma, small cell (oat cell) carcinoma, adenocarcinoma, and large cell (anaplastic) carcinoma.
Although the prognosis is usually poor, it varies with the extent of spread at the time of diagnosis and the growth rate of the specific cell type. Only about 13% of patients with lung cancer survive 5 years after diagnosis. Lung cancer is the most common cause of cancer death in men and is fast becoming the most common cause in women, even though it’s largely preventable. It’s associated with more cancer deaths per year than heart, colon, and prostate cancer combined.
Most experts agree that lung cancer is attributable to inhalation of carcinogenic pollutants by a susceptible host. Most susceptible are those persons who smoke or who work with or near asbestos.
Pollutants in tobacco smoke cause progressive lung cell degeneration. Lung cancer is 10 times more common in smokers than in nonsmokers; indeed, 80% of lung cancer patients are or were smokers.
Cancer risk is determined by the number of cigarettes smoked daily, the depth of inhalation, how early in life smoking began, and the nicotine content of the cigarettes. Two other factors also increase susceptibility: exposure to carcinogenic industrial and air pollutants (asbestos, uranium, arsenic, nickel, iron oxides, chromium, radioactive dust, and coal dust), and familial susceptibility.
Signs and symptoms
Because early-stage lung cancer usually produces no symptoms, this disease is typically in an advanced state at diagnosis. The following late-stage signs and symptoms commonly lead to a diagnosis:
with epidermoid and small cell carcinomas: smoker’s cough, hoarseness,
wheezing, dyspnea, hemoptysis, and chest pain
with adenocarcinoma and large cell carcinoma: fever, weakness, weight loss, anorexia, and shoulder pain.
Besides their obvious interference with respiratory function, lung tumors may also alter the production of hormones that regulate body function or homeostasis. Clinical conditions that result from such changes are known as hormonal paraneoplastic syndromes:
Gynecomastia may result from large cell carcinoma.
Hypertrophic pulmonary osteoarthropathy (bone and joint pain from cartilage erosion due to abnormal production of growth hormone) may result from large cell carcinoma or adenocarcinoma.
Cushing’s and carcinoid syndromes may result from small cell carcinoma.
Hypercalcemia may result from epidermoid tumors.
Metastatic signs and symptoms vary greatly, depending on the effect of tumors on intrathoracic and distant structures:
bronchial obstruction: hemoptysis, atelectasis, pneumonitis, and dyspnea
recurrent nerve invasion: hoarseness and vocal cord paralysis
chest wall invasion: piercing chest pain; increasing dyspnea; and severe shoulder pain, radiating down the arm
local lymphatic spread: cough, hemoptysis, stridor, and pleural effusion
phrenic nerve involvement: dyspnea; shoulder pain; and unilateral paralyzed diaphragm, with paradoxical motion
esophageal compression: dysphagia
vena caval obstruction: venous distention and edema of the face, neck, chest, or back
pericardial involvement: pericardial effusion, tamponade, and arrhythmias
cervical thoracic sympathetic nerve involvement: miosis, ptosis, exophthalmos, and reduced sweating.
Distant metastasis may involve any part of the body, most commonly the central nervous system, liver, and bone.
Typical signs and symptoms may strongly suggest lung cancer, but a firm diagnosis requires further evidence, including the following:
Chest X-ray usually shows an advanced lesion, but it can detect a lesion up to 2 years before symptoms appear. It also indicates tumor size and location.
Sputum cytology is marginally helpful in obtaining a diagnosis. It requires a specimen coughed up from the lungs and tracheobronchial tree, not postnasal secretions or saliva.
Computed tomography (CT) scan of the chest may help to delineate the tumor’s size and its relationship to surrounding structures.