LUNG CANCER
Most lung cancer originates in the cells of the lungs; however, cancer may also spread (metastasize) to the lung from other parts of the body.
Lung cancer is the most common cancer in both men and women. More importantly, it's the most common cause of death from cancer in both men and women.
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Causes
Cigarette smoking is the main cause of about 90 percent of lung cancer cases in men and about 70 percent of them in women. Lung cancer has become more common in women because more women are smoking cigarettes. The more cigarettes a person smokes, the greater the risk of lung cancer.
A small proportion of lung cancers (about 10 to 15 percent in men and 5 percent in women) are caused by substances encountered or breathed in at work. Working with asbestos, radiation, arsenic, chromates, nickel, chloromethyl ethers, mustard gas, and coke-oven emissions has been linked with lung cancer, although usually only in people who also smoke cigarettes. The role of air pollution in causing lung cancer is still uncertain. Exposure to radon gas in homes may be important in a small number of cases. Occasionally, lung cancers, especially adenocarcinoma and alveolar cell carcinoma develop in people whose lungs have been scarred by other lung diseases, such as tuberculosis and fibrosis.
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Types of Lung Cancer
More than 90 percent of lung cancers start in the bronchi (the large airways that supply the lungs): such cancer is called bronchogenic carcinoma. The types are squamous cell carcinoma, small cell (oat cell) carcinoma, large cell carcinoma, and adenocarcinoma.
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Alveolar cell carcinoma originates in the air sacs (alveoli) of the lung. Although this cancer can be a single growth, it often develops in more than one area of the lung at once.
Less common lung tumors are bronchial adenoma (which may be cancerous or noncancerous), chondromatous hamartoma (noncancerous), and sarcoma (cancerous). Lymphoma is a cancer of the lymphatic system. It may start in the lungs or spread to them.
Many cancers that start elsewhere in the body spread to the lungs. Cancers spread to the lungs most commonly from the breast, colon, prostate, kidney, thyroid, stomach, cervix, rectum, testis, bone, and skin.
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Symptoms
The symptoms of lung cancer depend on its type, its location, and the way it spreads. Usually, the main symptom is a persistent cough. People with chronic bronchitis who develop lung cancer often notice that their coughing becomes worse; if sputum can be coughed up, it may be streaked with blood. If the cancer grows into underlying blood vessels, it may cause severe bleeding.
The cancer may cause wheezing by narrowing the airway in which, or around which, it's growing. Blockage of a bronchus may lead to the collapse of the part of the lung that the bronchus supplies, a condition called atelectasis. Another consequence may be pneumonia with coughing, fever, chest pain, and shortness of breath. If the tumor grows into the chest wall, it may produce persistent chest pain.
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Symptoms that arise later include loss of appetite, weight loss, and weakness. Lung cancers often cause fluid accumulations around the lung (pleural effusions) that lead to shortness of breath. If cancer spreads within the lungs, severe shortness of breath, low levels of oxygen in the blood, and heart failure may develop.
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The cancer may grow into certain nerves in the neck, causing a droopy eyelid, small pupil, sunken eye, and reduced perspiration on one side of the face - together these symptoms are known as Homers syndrome. Cancers at the top of the lung may grow into the nerves that supply the arm, making the arm painful, numb, and weak. Nerves to the voice box may also be damaged, making the voice hoarse.
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A cancer may grow directly into the esophagus, or it may grow near it and put pressure on it, leading to difficulty in swallowing. Occasionally, an abnormal channel (fistula) between the esophagus and bronchi develops, causing severe coughing during swallowing because food and fluid enter the lungs.
A lung cancer may grow into the heart, causing abnormal heart rhythms, an enlargement of the heart, or fluid in the pericardial sac surrounding the heart. The cancer may grow into or around the superior vena cava (one of the large veins in the chest). Obstruction of this vein causes blood to back up in other veins of the upper body. The veins on the chest wall enlarge. The face, neck, and upper chest wallincluding the breasts swell and become tinged with purple. The condition also produces shortness of breath, headache, distorted vision, dizziness, and drowsiness. These symptoms usually worsen when the person bends forward or lies down.
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Lung cancer may also spread through the bloodstream to the liver, brain, adrenal glands, and bone. This may occur early in the disease, especially with small cell carcinoma. Symptomssuch as liver failure, confusion, seizures, and bone painmay develop before any lung problems become evident, making an early diagnosis difficult.
Some lung cancers produce effects far from the lungs, such as metabolic, nerve, and muscle disorders (paraneoplastic syndromes). These syndromes aren't related to the size or location of the lung cancer and don't necessarily indicate that the cancer has spread outside the chest; rather, they are caused by substances secreted by the cancer. These symptoms may be the first sign of cancer or the first indication that, cancer has returned after treatment. One example of a paraneoplastic syndrome is the Eaton-Lambert syndrome, characterized by extreme muscle weakness. Another example is the muscle weakness and soreness caused by inflammation (polymyositis), which may be accompanied by skin inflammation (dermatomyositis).
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Some lung cancers secrete hormones or hormonelike substances, resulting in abnormally high hormone levels. For example, small cell carcinoma tumors may secrete corticotropin, causing Cushing's syndrome, or antidiuretic hormone, causing water retention and low levels of sodium in the blood. Excessive hormone production can also cause the carcinoid syndrome- flushing, wheezing, diarrhea, and heart valve problems. Squamous cell carcinoma may secrete a hormonelike substance that leads to very high blood levels of calcium. Other hormonal syndromes linked to lung cancers include breast enlargement in men (gynecomastia) and an excess of thyroid hormone (hyperthyroidism). Skin changes, including darkening of the skin in the armpit, may also occur. Lung cancer can even change the shape of the fingers and toes and cause changes at the ends of long bones that can be seen on x-rays.
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Diagnosis
A doctor explores the possibility of lung cancer when a patient, especially a smoker, has a persistent or worsening cough or other lung symptoms. Sometimes a shadow on a chest x-ray of someone with no symptoms provides the first clue.
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A chest x-ray can detect most lung tumors, although it may miss small ones. However, an x-ray shows only a shadow in the lung, which isn't proof of cancer. Usually, a microscopic examination of a tissue specimen is needed. Sometimes, a sample of coughed-up sputum can provide enough material for such an examination (called sputum cytology). Or bronchoscopya may be performed to obtain tissue. If the cancer is too deep in the lung to be reached with a bronchoscope, a doctor can usually obtain a specimen by inserting a needle through the skin while using computed tomography (CT) for guidance; (his procedure is called a needle biopsy. Sometimes, a specimen can be obtained only by a surgical procedure called a thoracotomy.
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CT scanning may show small shadows that don't appear on chest x-rays. The CT scans also can reveal whether the lymph nodes are enlarged; however, a biopsy (removal of a specimen for microscopic examination) often is needed to determine if the enlargement results from inflammation or cancer. CT scans of the abdomen or head may show that the cancer has spread to the liver, adrenal glands, or brain. A bone scan may show that it has spread to the bones. Because small cell carcinoma tends to spread to the bone marrow, a doctor sometimes performs a bone marrow biopsy (removal of a specimen for microscopic examination).
Doctors categorize cancers 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 patient's prognosis.
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Treatment
Noncancerous bronchial tumors are usually removed surgically because they may block the bronchi and may become cancerous over time. Often a doctor can't be sure if a tumor at the edge of the lungs is cancerous until it has been removed and examined microscopically.
For cancer other than small cell carcinoma that hasn't spread beyond the lung, surgery is sometimes possible. Although 10 to 35 percent of cancers can be removed surgically, removal doesn't always result in a cure. Among people who have an isolated, slow-growing tumor removed, 25 to 40 percent survive at least 5 years after the diagnosis. Survivors must have regular checkups because lung cancer recurs in 6 to 12 percent of people who have undergone surgery. The percentage is much higher for those who continue to smoke after surgery.
Before surgery a doctor performs pulmonary function tests to determine if the remaining lung can provide enough function. If the test results are poor, surgery may not be possible. The amount of lung to be removed is decided during surgery, with the amount varying from a small part of a lung segment to an entire lung.
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Occasionally, cancer that begins elsewhere and spreads to the lungs is removed form the lungs after being removed at the source. This procedure is recommended rarely, and only about 10 percent of people who have it survive 5 years or more.
If cancer has spread beyond the lungs, if the cancer is too close to the trachea, or if the person has other serious conditions (such as severe heart or lung disease), surgery isn't useful. Radiation therapy may be given to people who can't undergo surgery because they have another serious disease. In such cases the radiation therapy isn't intended to cure but to slow the growth of the cancer. Radiation therapy also is useful for controlling bone pain, superior vena cava syndrome, and spinal cord compression. However, the therapy can cause inflammation in the lungs (radiation pneumonitis), which produces coughing, shortness of breath, and fever. The symptoms may be relieved with corticosteroids, such as prednisone. For lung cancer other than small cell carcinoma, no chemotherapy regimens are particularly effective.
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Because small cell carcinoma of the lung has almost always spread to distant parts of the body by the time of diagnosis, surgery isn't an option. Instead, the cancer is treated with chemotherapy, sometimes coupled with radiation treatment. In about 25 percent of patient chemothereapy substantially prolongs survival. People with small cell carcinoma of the lung who have been well responding to chemotherapy may benefit from radiation treatment to the head to treat cancer that has spread to the brain.
Many people with lung cancer experience a substantial decrease in lung function, whether or not they undergo treatment. Oxygen therapy and drugs that widen the airways may ease breathing difficulties. Many people with advanced lung cancer develop such pain and difficulty in breathing that they require large doses of narcotics in the weeks or months before their death. Fortunately, narcotics can help substantially if used in adequate doses.
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