Lung cancer caused by smoking

Americans are known the world over as preventive health enthusiasts. We jog for fitness, floss and take fluoride to prevent tooth decay, and eat low-fat products to reduce the risk of heart disease. Even the rarest environmental pollutant is likely to provoke public outrage and regulatory action if it is found to increase cancer risk.

Yet it's not uncommon for people who engage in such healthful activities to also engage in another activity known unmistakably to cause lung cancer: cigarette smoking.

Lung cancer is the leading cause of cancer death in this country. The lung cancer death rate recently surpassed that of breast cancer in women, according to the national Centers for Disease Control and Prevention, and continues to climb. Yet the vast majority of lung cancer cases are highly preventable.

FDA is responsible for ensuring the safety and effectiveness of the devices or drugs used to diagnose or treat lung cancer.

Smoke Gets in Your Lungs

The constant assault of cigarette smoke wears away cilia, the tiny hairlike structures that line the lungs' air passages and sweep out foreign material trapped inside by mucus. Without this cleaning mechanism, the lungs are particularly vulnerable to compounds brought into air passages. Most lung cancers crop up in the cells that are directly exposed to inhaled air.

People who smoke or who live with a smoker breathe air that may harbor more than 50 cancer-fostering chemicals, including benzopyrene and formaldehyde, as well as a radioactive compound called polonium-2 I 0. One researcher, in the September 1993 edition of the journal Pediatrics, estimates that the lungs of a person who smokes a pack of cigarettes a day, are exposed to as much radiation a year as they would absorb from 250 chest x-rays.

The risk of developing lung cancer increases with the number of cigarettes smoked and the number of years of smoking. People who smoke filtered low-tar cigarettes may have a somewhat lower lung cancer risk than those who smoke regular cigarettes. However, according to the National Cancer Institute (NCI), people may smoke more cigarettes if the nicotine content is reduced (as it is in low-tar cigarettes), so these smokers still have a substantial risk of lung cancer.

Cigar and pipe smoking can also boost the risk of developing lung cancer, but because people usually inhale less smoke with this type of tobacco use, it is not as high a lung cancer risk as cigarette smoking. However, these forms of smoking, as well as chewing tobacco, cause other types of cancer. The tobacco smoke nonsmokers breathe, also called secondhand smoke," has been classified by the Environmental Protection Agency as one of the most dangerous environmental contaminants.

Other Causes of Lung Cancer

Exposure at high levels to certain compounds encountered in various mining or manufacturing jobs also can trigger lung cancer. These compounds include asbestos, nickel, chromium, coal gas, mustard gas, arsenic, vinyl chloride, beryllium, hydrocarbons, ionizing radiation, and the radon byproducts of uranium mining.

Such compounds are more apt to cause lung cancer in smokers than nonsmokers. Asbestos workers who smoke cigarettes, for example, are 30 times more likely to develop lung cancer than asbestos workers who don't smoke. They have 90 times the lung cancer risk of people who neither smoke nor work with asbestos, according to NCI.

Although radon produced by the decay of uranium in soil and rocks is present in low levels in many houses, it is not certain whether such low-level radon exposure can cause lung cancer.

Some smokers may feel they are genetically protected from lung cancer because their mothers or fathers smoked and never got the disease. But this could be "a fatal mistake," points out M. Miles Braun, M.D., a senior research investigator at NCI. His recent study of twins suggests that for most people, heredity plays little or no role in the development of lung cancer.

The study found that pairs of identical twins died less often of lung disease than pairs of fraternal twins. This finding is opposite what would be expected if a susceptibility to lung cancer was inherited because fraternal twins share only some of the same genes, unlike identical twins, who inherit identical genes.

There also is no firm evidence that vitamin supplements can protect smokers from the disease. According to NCI, some human studies suggest smokers might be able to lower their risk of lung cancer by eating more fruits and vegetables. More studies need to be done, however, to confirm this hypothesis.

By far the most effective way to avoid lung cancer is to steer clear of tobacco smoke, experts agree. Studies show that lung cancer risk gradually declines after stopping smoking. One study cited by CDC found that 10 years after quitting smoking, people who had smoked for less than 20 years had almost the same risk of lung cancer as lifelong nonsmokers.

Difficult to Detect

Few cases of lung cancer are detected early enough to achieve the best response to treatment. Coughing and wheezing are the earliest symptoms. But these respiratory annoyances are often dismissed as "smoker's cough" - the hacking many smokers have because smoking prompts their lungs to produce excess mucus - or chronic bronchitis, to which smokers are also prone.

Other early symptoms of lung cancer include coughing up blood, chest pain, and shortness of breath. People with lung cancer may also experience repeated bouts of pneumonia or bronchitis, fever, weakness, weight loss, hoarseness, or swelling of the neck and face.

In some cases, patients first notice symptoms stemming from the spread of the cancer to the brain, bones, or other organs. These symptoms include headaches, blurred vision, dizziness, unsteadiness or difficulty walking, and bone pain.

Sometimes symptoms may be caused by hormones made by lung cancer cells. Certain lung cancer cells, for example, produce a hormone that causes a sharp drop in the level of salt in the body. This can produce many symptoms, including concentrated urine, confusion, fatigue, or coma.

Doctors diagnose the presence, type or extent of lung cancer with a series of tests. The first is a chest x-ray to detect any abnormal spots on the lungs. Doctors may also require other x-ray tests, such as a tomogram or a CT (computed tomography) scan. Tomograms image thin slices of the lung that can show a small cancer not seen on standard x-rays. CT scans produce an image of a cross-sectional slice of a selected body area and are particularly useful for showing the extent of a lung tumor and whether it has spread into neighboring organs.

Sometimes doctors can detect lung cancer cells in the patient's sputum, examined under a microscope. Additional tests are usually required to determine the tumor's type and location. Doctors usually need to extract cells from the lungs to screen under a microscope for cancer cells. A procedure called a bronchoscopy allows doctors to pluck cells from the inner walls of the bronchi-the two branches of the trachea (windpipe) leading to the lungs. This procedure is generally done in a hospital. The patient is given a local anesthetic, and a flexible thin tube with lighting and magnifying devices called a bronchoscope is threaded through the nose or mouth into the lung.

To collect cells hard to reach with a bronchoscope, doctors perform a needle aspiration biopsy guided by fluoroscopy. Fluoroscopy is an x-ray procedure that uses a television screen to view internal organs such as the heart and lungs while they are in motion. Using the picture on the screen as a guide, the doctor inserts a long, thin needle into the tumor to withdraw cells for examination.

If lymph nodes in the neck seem enlarged, doctors may remove them to see if cancer cells have spread there. Doctors may also biopsy the lymph nodes between the lungs. Tissue is removed through a small incision in the chest while the patient is under general anesthesia.

Radionuclide scans are sometimes done to find out whether lung cancer has spread to other areas of the body. Technicians inject patients with a small amount of radioactive material. These compounds emit signals a machine translates into a screen image that outlines areas of possible cancer involvement in the bones or other parts of the body.

Spreads Rapidly

Unfortunately, in about 85 percent of patients, by the time lung cancer is diagnosed the disease has spread beyond the lungs. Lung cancers tend to spread more quickly than most other types of cancer because the lungs are richly supplied by the blood and lymph systems, which carry cells to other parts of the body. This makes lung cancers particularly difficult to treat.

The three main weapons doctors can wield against lung cancer are surgery, radiation directed at the chest, and chemotherapy with anti-cancer drugs.