What Is Lung Cancer?

What Is Lung Cancer?

Although lung cancer is the leading cause of cancer death in the U.S. in both men and women, it is also one of the most preventable kinds of cancer. At least four out of five cases are associated with cigarette smoking, and the cause-and-effect relationship has been extensively documented. During the 1920s, large numbers of men began to smoke cigarettes, presumably in response to increased advertising. Twenty years later, the frequency of lung cancer in men climbed sharply. In the 1940s, significantly more women became smokers. Twenty years later, there was a similar dramatic increase in lung cancer among women.

 

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 cancerous tumors that originate in the lung itself -- primary lung cancer -- have been identified. The major types of lung cancer are small-cell lung cancer and non-small cell lung cancer. The more common non-small cell variety is further divided into squamous cell carcinoma, adenocarcinoma, large-cell carcinoma, and more. Mixed tumors may also occur.

Non-Small Cell Lung Cancer

Squamous cell carcinoma usually starts in cells of the central bronchi, the largest branches of the bronchial tree. It accounts for 30% of lung cancers, and occurs more commonly in men and in smokers. It's the easiest to detect early, since its distinctive cells are likely to show up in tests of mucus samples. It also tends to be most curable if found early because it spreads relatively slowly and often does not spread outside of the lung.

Adenocarcinoma is the most common type of lung cancer accounting for 40% of all cases with its incidence increasing. It is most commonly seen in women and nonsmokers. It tends to originate along the outer edges of the lungs in the smaller airways. Adenocarcinoma tends to spread to the lymph nodes and distant organs. It's commonly a mixed type of tumor and may cause no symptoms initially.   

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 accounting for 10%-15% of all cases. However, this type of tumor has a high tendency to spread to nearby lymph nodes and distant sites.

Small Cell Lung Cancer

Small-cell lung cancer is the most aggressive form of lung cancer. This cancer usually originates in the large, central bronchi. It spreads quickly, usually within 90 days, often before symptoms appear, making it particularly threatening. In fact, in up to 75% of patients with this type of cancer, the disease has spread by the time it’s diagnosed. It frequently spreads (metastasizes) to the liver, bone, and brain. Although responsive to chemotherapy, small-cell lung cancer is rarely associated with long-term survival.

About 226,000 people in the U.S. will be diagnosed with lung cancer in 2012. It is the second most common cancer in both men and women. However, it is the leading cause of cancer deaths in both sexes -- killing over 160,000 people each year. 

An individual cancer sufferer's prognosis will vary according to the type of lung cancer involved, the person's overall health, and the stge of the cancer at the time of initial diagnosis.

What Causes Lung Cancer?

About 85% of lung cancer is caused by smoking and, as with any cancer, each person's genetics. The fact that lung cancer runs in some families suggests that a predisposition can be inherited. Additionally, certain genetic traits have been identified that make some people more susceptible than others to cancer-causing substances like those found in tobacco smoke.

Nonetheless, anyone who smokes one pack of cigarettes daily is 20 times more likely than a nonsmoker to develop lung cancer. For people who smoke more than two packs a day, the risk more than triples. Breaking the smoking habit reduces risk significantly, yet former smokers are always slightly more susceptible than nonsmokers. Secondhand tobacco smoke can also cause lung cancer, giving nonsmokers who live or work with smokers a somewhat higher lung cancer risk than those in smoke-free environments. In fact, approximately 3,000 people die each year of lung cancer associated with second hand smoke exposure. And those living in a home with a smoker have a 30% higher risk of developing lung cancer than in a smoke-free home. 

Cancer-causing substances other than those found in tobacco or tobacco smoke can also cause lung cancer if inhaled over time. However, experts disagree about how much exposure to specific cancer-causing substances is dangerous. Workers who are exposed on a daily basis to asbestos have a 90-fold increase of getting lung cancer when compared to non-exposed persons. Workers exposed to uranium dust or the radioactive gas radon are also much more likely than the average person to develop lung cancer, especially if they are smokers.

Lung tissue that has been scarred by disease or infection, such as scleroderma or tuberculosis, is more susceptible to tumor growth within the scar tissue (called a scar carcinoma). Because of a high frequency of lung cancer among people who eat large amounts of fat and cholesterol, some researchers speculate that diet may also influence lung cancer risk.