Cancer, Lung

Risk: The greatest risk factor for lung cancer is tobacco smoke; 87% of lung cancers are thought to be caused by smoking, or by secondhand smoke ("Detailed Guide"). A diet low in fruits and vegetables can also increase the risk for lung cancer when concurrent in individuals who smoke or who are exposed to smoking. Those that stop smoking cigarettes, pipes, cigars, or marijuana can reduce their risk of lung cancer by one-third. Individuals who are exposed to smoking in the workplace have an increased risk for developing lung cancer.

Other risk factors include exposure to certain industrial agents, such as asbestos, arsenic, gasoline, ionizing radiation, nickel, aromatic hydrocarbons, and indoor air pollutants such as radon gas. There may also be a genetic predisposition to lung cancer.

Men have a 1 in 13 chance of developing lung cancer, and women a 1 in 18 chance ("Detailed Guide"). Lung cancer is unusual in individuals under 45 years of age; the average age at diagnosis with lung cancer is 70 years ("Detailed Guide").

Incidence and Prevalence: Lung cancer is the leading cause of cancer mortality in both men and women in the US. It is estimated that in 2005 there will be more than 170,000 new cases diagnosed, accounting for about 13% of all cancers ("Detailed Guide"). More individuals die from lung cancer than from breast, prostate, and colon cancers combined. The predicted mortality in 2005 is greater than 160,000 deaths, accounting for about 28% of all cancer-related deaths ("Detailed Guide"). Lung cancer is increasing worldwide at a rate of 0.5% per year, possibly due in part to increase of smoking in developing countries and industrial exposure. In all countries, rates are higher in urban than rural areas, and 2 to 6 times higher in males than females. In European countries, it is the leading cause of cancer incidence and mortality and accounts for about 21% of all cancer cases in men.

History: Individuals may report persistent cough, coughing up blood (hemoptysis), shortness of breath (dyspnea), chest pain, loss of appetite and weight loss, hoarseness, and bone pain. The bone pain can manifest anywhere in the body because of the ability of the lung cancer to spread. There may be recent history of a recurrent infection such as bronchitis or pneumonia; sometimes lung cancer goes undiscovered until the individual is treated for one of these conditions. Individuals may have a history of smoking or exposure to industrial carcinogens. In the vast majority of cases, the cancer will have metastasized into adjacent tissues and organs (advanced stage) by the time it is first diagnosed.

Physical exam: Findings may be variable and depend on the stage of the disease and the extent of local, regional, or distant spread of the cancer. Physical examination of the chest and lungs may be normal. Wheezing or the absence of breath sounds in part of the lungs can indicate partial or total obstruction of the airways. An enlargement of the lymph nodes around the neck and collarbones or localized chest tenderness may indicate spread of the cancer to these areas (metastatic cancer).

If lung cancer tumors affect the upper lung(s), nearby nerves that pass from the neck to the upper chest may become damaged, causing severe shoulder pain (Horner's syndrome, Pancoast tumors). Other signs of Horner's syndrome include drooping of one eyelid (ptosis), reduced/absent perspiration on one side of the face, and a smaller (constricted) pupil of the eye on the same side.

Other lung cancer-related syndromes include tumor-related (paraneoplastic) syndromes, in which hormones or hormone-like substances are released by the cancer cells into the bloodstream, affecting other organs or tissues. Problems with these distant organs or tissues may be the first sign of lung cancer, but can confound even the most astute clinician by mimicking other diseases. Examples of SCLC paraneoplastic syndromes include those that cause low levels of antidiuretic hormone, those that produce blood clots in the legs and internal organs, and those that impair cerebellar function. Examples of NSCLC paraneoplastic syndromes include those that cause hypercalcemia, extra bone growth (hypertrophic osteoarthropathy), blood clot formation, and gynecomastia.

Tests: A chest x-ray is the primary tool for diagnosing lung cancer and is especially helpful if previous chest x-rays are available for comparison. The sputum may be examined microscopically for cancer cells (sputum cytology). If cancer cells are not found, the area of a suspected tumor is directly viewed through a flexible tube (bronchoscopy) and a tissue sample (biopsy) taken for examination under a microscope. A needle biopsy may be performed if the tumor is beyond reach of the bronchoscopy procedure. Bone marrow biopsy is used to sample the bone marrow for metastasized cancer cells of SCLC. A biopsy may also be taken on occasion through a tube passed by a chest surgeon into a portion of the chest (mediastinum) using a procedure called mediastinoscopy; this procedure is performed under a general anesthesia. Thoracoscopy may also be performed under general anesthesia to visualize the pleural cavity and remove a biopsy sample. If pleural effusion is present, a procedure to drain the pleural fluid and sample it for cancer cells may be useful (thoracentesis).

CT of the chest, abdomen, and brain allow further evaluation of general x-ray findings. CT may also help identify the position of the tumor more precisely and whether the cancer has metastasized. Positron emission tomography (PET) can be used to detect early stage lung cancer and/or to identify regions of metastasis. MRI may be used to visualize the spread of cancer to the brain or spinal cord. A radioactive substance can be injected and pictures taken (bone scintigraphy) to determine if the cancer has metastasized to the bone. Blood tests to measure complete blood count (CBC), electrolytes, serum calcium, liver function, and kidney function may be performed to evaluate whether the lung cancer has metastasized.