Lung Cancer

Lung cancer is one of the most common types of cancer, and it causes the most deaths from cancer in both men and women. The chance of developing lung cancer increases with age. Lung cancer is more common in men than in women, but the frequency is increasing in women because more women are smoking.

Lung cancer that begins in the lungs is called primary lung cancer; cancer that begins elsewhere in the body and spreads to the lungs is called metastatic lung cancer. Metastatic cancers spread to the lungs most commonly from breast, colon, and prostate cancers.

Most primary lung cancers develop in the larger airways (bronchi). A few develop in the air sacs (alveoli). The two main types of primary lung cancers are small cell cancers and non-small cell cancers. Other types of lung cancers include bronchial carcinoids and sarcomas. Cancer of the lymphatic system (lymphoma) may also start in the lungs.

Causes

Cigarette smoking causes most lung cancers. Cigar and pipe smoking can also cause lung cancer. The more a person has smoked and the longer a person has smoked, the greater is the risk of developing lung cancer. About 10% of smokers eventually develop lung cancer.

Much less often, lung cancer is caused by substances such as asbestos and arsenic. The risk of developing lung cancer is especially high in people who have been exposed to these substances and who also smoke. Air pollution and exposure to radon gas in homes may cause a small number of lung cancers. Occasionally, lung cancers develop in people whose lungs have been scarred by other diseases, such as tuberculosis.

Symptoms

The symptoms of lung cancer depend on its type and location and the way it spreads. A very common symptom, and often the first to develop, is a persistent cough. People who have chronic bronchitis or another lung disease that produces coughing often notice their coughing becoming worse if lung cancer develops. Sputum may be streaked with blood. If lung cancer grows into a blood vessel, it may cause severe bleeding.

Lung cancer may cause wheezing, either by growing inside an airway or by growing very near an airway and compressing it. The airway may become partially or completely blocked. Blockage of an airway can lead to collapse of part of the lung, a condition called atelectasis. A blocked airway may also cause shortness of breath and pneumonia, with coughing, fever, and chest pain.

Symptoms of lung cancer that usually develop later include fatigue, weakness, loss of appetite, and weight loss. Severe shortness of breath may develop if cancer spreads widely within the lungs. Fluid may accumulate around the lung (pleural effusion) if the cancer spreads into the space between the lungs and the chest wall (pleural space). Pleural effusions can produce shortness of breath.

Persistent chest pain may develop if lung cancer grows into the tissues of the chest wall. Lung cancer may also grow into certain nerves in the neck, causing a condition called Horner's syndrome. Symptoms of Horner's syndrome include a droopy eyelid, a pupil that cannot dilate (stays small) in the dark, a sunken appearance of the eye, and decreased sweating on one side of the face. Cancers at the top of the lung (the portion closest to the collar bone) may grow into the nerves that supply the arm, making the arm painful, numb, and weak—this combination of symptoms is called Pancoast syndrome. The voice can become hoarse if cancer compresses and damages the nerves of the voice box.

Difficulty swallowing may develop if lung cancer grows into or very near the esophagus. Occasionally, lung cancer causes an abnormal channel (fistula) to develop between the esophagus and an airway. Such a fistula can cause severe coughing during swallowing, because food and fluid enter the lungs.

Lung cancer may grow into the heart, causing abnormal heart rhythms, blocking blood flow through the heart, or causing fluid to build up in the sac that surrounds the heart (pericardium). The cancer may grow into or compress the superior vena cava, the large vein in the chest that carries blood back to the heart. Blockage of this vein causes blood to back up in other veins of the upper body; this condition is called superior vena cava syndrome. The blood causes the face, neck, and upper chest wall to swell; sometimes shortness of breath, headache, impaired vision, dizziness, and drowsiness occur.

Lung cancer can spread through the bloodstream to the liver, brain, adrenal glands, spinal cord, bones, and other parts of the body. The spread of lung cancer may occur early in the disease, especially with small cell cancer. Symptoms—such as headache, confusion, seizures, and bone pain—may develop even before lung problems become noticeable.

Screening and Diagnosis

There is no good way to screen for lung cancer. People with a very high risk of developing it may undergo periodic tests, but most lung cancers are missed anyway.

A doctor suspects lung cancer when a person, especially a smoker, has a persistent or worsening cough, shortness of breath, or coughed-up sputum tinged with blood. Sometimes a shadow on a chest x-ray taken to evaluate cough or some other symptom provides the first clue, although such a shadow is not proof of cancer.

Computed tomography (CT) may show small nodules that are not apparent on chest x-rays. Positron emission tomography (PET) and a certain type of CT called spiral CT may improve the ability to detect small cancers. CT can also reveal whether the lymph nodes are enlarged; a biopsy of enlarged lymph nodes is often needed to determine if cancer is the cause of the enlargement.

Doctors usually need to examine sputum or a sample of lung tissue to confirm the diagnosis. A flexible viewing tube called a bronchoscope can be used to look inside airways and obtain tissue for examination under a microscope. If the cancer is too deep in the lung to be reached with a bronchoscope, a doctor can usually obtain a sample of tissue by inserting a needle through the skin while using CT to guide movements of the needle. This procedure is called a needle biopsy. Sometimes, a specimen can be obtained only through an opening in the chest wall, in a procedure called a thoracotomy.

A CT scan of the abdomen or head may be done to determine if lung cancer has spread, especially to the liver, adrenal glands, or brain. A bone scan may show that it has spread to the bones. In people with small cell cancer, a bone marrow biopsy is sometimes done, because this type of cancer tends to spread to the bone marrow.

Cancers are categorized based on how large the tumor is, whether it has spread to nearby lymph nodes, and whether it has spread to distant organs. The different categories are called stages. The stage of a cancer suggests the most appropriate treatment and enables a doctor to estimate the person's outlook.

Prevention and Treatment

Prevention of lung cancer includes quitting smoking and avoiding exposure to potentially cancer-causing substances in the environment.

Surgery is the best treatment for nonsmall cell lung cancers that have not spread beyond the lungs. However, surgery is unlikely to be helpful if the cancer has spread beyond the lungs, if the cancer is too close to very large airways (the trachea or its two main branches), or if the person has another potentially life-threatening disorder (such as severe coronary artery disease or chronic obstructive pulmonary disease).

Before surgery, a doctor estimates how much lung tissue needs to be removed and how much lung tissue will be left. Depending on how far the cancer has spread, the amount varies from a small part of a lung to an entire lung. Tests are then done to determine if the amount of lung tissue estimated to be left after surgery will be enough to ensure adequate lung function. If these tests indicate that removing the cancerous part of the lung will result in inadequate lung function, surgery is not possible.

Removal of the cancer does not always result in a cure. The extent of cancer in the lung and identification of all areas where a cancer has spread cannot always be determined. Therefore, many people who undergo surgery eventually die from their cancer, either in the lung or at another site. Survivors must have regular checkups, including periodic chest x-rays and CT scans.

For nonsmall cell lung cancers, results of surgery may be improved by chemotherapy and radiation therapy given before and after surgery.

Radiation therapy may also be given to people who choose not to have surgery, who cannot undergo surgery because they have another serious condition, or whose cancer has spread. Although radiation therapy usually only partially shrinks the cancer or slows its growth, it may halt growth for a prolonged period in 10 to 15% of them. Combining chemotherapy with radiation therapy may provide further benefit. Radiation therapy is also useful for controlling symptoms that develop from complications of lung cancer, such as coughing up blood, bone pain, superior vena cava syndrome, and pressure on nerves.

The effectiveness of chemotherapy alone for nonsmall cell lung cancer is not very good. If nonsmall cell lung cancer has spread, some people live several more months when given chemotherapy.

Chemotherapy, sometimes coupled with radiation therapy, is the treatment of choice for small cell cancer because the cancer has almost always spread to other parts of the body by the time it is diagnosed. In about 25% of people, chemotherapy substantially prolongs survival and may occasionally cure these people. Without chemotherapy, only half of the people with small cell cancer survive 4 months. However, chemotherapy often causes many side effects that can make people feel very ill. People with small cell cancer who have been responding well to chemotherapy may benefit from radiation therapy to the head to treat cancer that may have spread to the brain. Sometimes lung cancer spreads to the brain early enough that no symptoms are apparent and nothing abnormal can be seen on a CT or MRI scans of the head.

Other treatments are often needed to relieve symptoms. Because many people with lung cancer have a decrease in lung function, oxygen therapy and bronchodilators (drugs that widen the airways) may help breathing. Advanced lung cancer may cause such intense pain and difficulty in breathing that many people require large doses of opioids in the weeks or months before their death. Fortunately, opioids can control pain if adequate doses are used.

Outlook

Lung cancer has a poor outlook. On average, people with untreated lung cancer survive little more than 6 months. Overall, even with therapy, fewer than 15% of people survive for 5 or more years. Because small cell cancer has almost always spread beyond the lung at the time of diagnosis, its outlook is worse than for other types of lung cancer.