The Basics of Lung Cancer

For many years, lung cancer was a man's disease. Reading lung cancer information has led us to today. Lung cancer is the most common cancer-related cause of death among men and women alike. More lung cancer info has turned up the fact that in 1987, lung cancer surpassed breast cancer to become the leading cause of cancer death among US women.

By 2002 there were about 169,400 new cases of lung cancer in the U.S., accounting for about 13 percent of all cancers: 90,200 among men and 79,200 among women. According to the American Cancer Society, this year, about 154,900 people will die of this disease: 89,200 men and 65,700 women.

Lung cancer occurs most often in people over 50 who have long histories of cigarette smoking. The incidence of lung cancer in women as a whole has climbed at an alarming rate. Since 1950, lung cancer mortality rates for U.S. women have increased an estimated 600 percent. These increases are clearly attributable to the increases in the number of women who have smoked.

Normal lung tissue is made up of cells that are programmed by genes to create tissue in a certain shape and to perform certain functions. Lung cancer develops when the genetic material responsible for production of these cells is damaged. This damage is known as genetic mutations. Lung cancer results as the uncontrolled growth of abnormal cells in the lung. Repeated exposure to carcinogens, such as tobacco smoke, causes the mutations.

Mutations in the genetic material of the lung cells cause the instructions for those cells to go awry. Consequently, those cells and their offspring reproduce at a dramatic pace, without regard for the normal shape and function of a lung. That wild reproduction causes the formation of tumors that may block air passages in the lung and make it stop functioning as it should. Mutations may also prevent normal programmed cell death, thereby adding to the accumulation of cells, and tumor formation.

Some genes are known as tumor suppressors. Their job is to keep abnormal cells from growing and forming tumors. Researchers have determined that a tumor suppressor gene called p53 is almost always defective in cases of small-cell lung cancer, and in approximately half of non-small cell lung cancer cases. Because of the defect in the gene, it does not stop the reproduction of tumor cells as it should.

The Basics of Lung Cancer (cont.)

Some women inherit genes from their parents that are more resistant to damage and cancer than others. Those whose genes do not provide as much protection against cancer are said to be genetically susceptible to the disease. Scientists have shown that some cancers (i.e. breast cancer) involve genes that are passed down from parents to their children, but the link to heredity has not been absolutely confirmed in lung cancer.

What we do know is that smoking is the number one cause of lung cancer. Cigarette smoke contains more than 4,000 different chemicals, many of which are proven carcinogens, while hundreds of others increase the cancer-causing power of carcinogens. Women who smoke are estimated to be 12 times more likely to get cancer than those who don't.

The more you smoke and the longer you smoke, the greater your risk of lung cancer. But if you stop smoking, the risk of cancer decreases steadily each year as abnormal cells are replaced by normal cells. It never returns completely to the risk of people who have never smoked, however, and lung cancer has become, in large measure, a disease of former smokers.

Radon, by its own action and by its interaction with cigarette smoking, is the second-most important risk factor for lung cancer in the U.S., according to the American Cancer Society. Radon is a radioactive gas that is found in the earth's rocks and soil. It is formed by the natural breakdown of radium, which is a radioactive product of decaying uranium. Radon problems have been identified in every state. This invisible, odorless gas can enter homes from the soil under foundations. Lung cancer risk is increased when radon levels are present at high levels in the home and exposure occurs over a long period of time, according to the American Cancer Society. Radon levels in the home can be measured with test kits available in hardware stores. Homeowners also can hire a company with experience in checking radon levels. Testing should be done more than once to average the results.

Another leading cause of lung cancer is on-the-job exposure to carcinogens. Asbestos is perhaps the best known of the industrial substances associated with lung cancer, but there are many cancer-causing substances that people may deal with at work. Some others are uranium, arsenic and certain petroleum products.

The Basics of Lung Cancer (cont.)

Lung cancer takes years to develop. After exposure to carcinogens, a few unusual cells begin to develop. With continued exposure, more abnormal cells appear. These cells may be on their way to becoming cancerous and forming a tumor. Lung tumors almost always start in the spongy, pinkish gray walls of the bronchi — the tubular, branching airways of the lungs. More than 20 types of malignant tumors that originate in the lung itself — primary lung cancer — have been identified. The major types are small-cell lung cancer and non-small cell lung cancer. The more common non-small variety is divided into:

Adenocarcinoma — the most common type of lung cancer — tends to originate along the outer edges of the lungs in the small bronchi or smaller bronchioles. Adenocarcinoma often spreads to spaces between the lungs and the chest wall, and its typical location makes early detection difficult. Adenocarcinoma often presents as a metastasis (site of cancer spread) in the brain or in a bone, before the patient has any symptoms in the chest.
Squamous cell carcinoma usually starts in cells of the central bronchi, the largest branches of the bronchial tree. It is the easiest to detect early, since its distinctive cells are likely to show up in tests of sputum samples. It also tends to be most curable if found early because it spreads relatively slowly.
Large-cell carcinomas are a group of cancers with large, abnormal-looking cells that tend to originate along the outer edges of the lungs. They are the least common of the non-small-cell lung cancers.

Small-cell lung cancer is the most aggressive form of the disease; it is also called oat-cell cancer because, under a microscope, its cells resemble oat grains. Like squamous cell carcinoma, this cancer usually originates in the central bronchi. It spreads quickly, often before symptoms appear, making it particularly threatening. It frequently spreads (metastasizes) to the liver, bone and brain. Although responsive to chemotherapy, small cell lung cancer is less frequently cured because it usually is not discovered before it has spread.

The Basics of Lung Cancer (cont.)

The symptoms of the cancer vary depending on several factors, including where in the lung the tumor is found. If the cancer is located in one of the bronchi, it can irritate the lining of the bronchus (one of the main airways that branches off of the trachea or windpipe) and cause a chronic cough. The cancerous area may bleed when a person coughs.

If the tumor grows larger, it may gradually fill the bronchus so that air can't pass in or out. A blocked bronchus may also cause repeated lung infections or pneumonia.

A tumor located in the outer part of the lung may not produce any symptoms until it is fairly large. Sometimes the first sign may be chest pain from the tumor growing into the lining of the lungs or the ribs and muscle of the chest wall.

A person's lungs have extensive networks of blood and lymph vessels. Cancer cells may grow into these vessels and be carried by the blood or lymph to circulate through the body. The cancer cells may then be deposited in other organs of the body. A new colony of cancer cells, which started in another organ, is known as metastasis.

The first site of tumor metastasis is usually the lymph nodes within the lungs and the mediastinum (the space between the two lungs in the middle of the chest).

It is possible for cancer cells that begin in other organs to spread to the lungs. These cases are very different medical problems, however. Depending on the organ of origin, such cases might be termed "primary breast cancer, metastatic to the lungs," or "primary kidney cancer, metastatic to the lungs."