What is lung cancer?
Cancer is a class of diseases characterized by out-of-control cell growth, and lung cancer occurs when this uncontrolled cell growth begins in one or both lungs. Rather than developing into healthy, normal lung tissue, these abnormal cells continue dividing and form lumps or masses of tissue called tumors. Tumors interfere with the main function of the lung, which is to provide the bloodstream with oxygen to be carried to the entire body. If a tumor stays in one spot and demonstrates limited growth, it is generally considered to be benign.

More dangerous, or malignant, tumors form when the cancer cells migrate to other parts of the body through the blood or lymph system. When a tumor successfully spreads to other parts of the body and grows, invading and destroying other healthy tissues, it is said to have metastasized. This process itself is called metastasis, and the result is a more serious condition that is very difficult to treat.

Lung cancer is called "primary" if the cancer originates in the lungs and "secondary" if it originates elsewhere in the body but has metastasized to the lungs. These two types are considered different cancers from diagnostic and treatment perspectives.

What are the symptoms of lung cancer?
Lung cancer may cause a number of symptoms. A cough is one of the more common ones and is likely to happen when a tumor grows and blocks an air passage. Another symptom is chest, shoulder, or back pain, which feels like a constant ache that may or may not be related to coughing. Other symptoms may include shortness of breath, fatigue, repeated pneumonia or bronchitis, coughing up blood, hoarseness, or swelling of the neck and face.

There may also be symptoms that do not seem to be at all related to the lungs. These may be caused by the spread of lung cancer to other parts of the body. Depending on which organs are affected, symptoms can include headaches, weakness, pain, bone fractures, bleeding, or blood clots.

What are the different types of lung cancer?

The type of cells found in a tumor determines the kind of cancer. The two main types of lung cancer are small cell and nonsmall cell. The terms small cell and nonsmall cell refer to the type of cell a doctor can see under the microscope, not to the size of the tumor. There are more than a dozen different kinds of lung cancer.

The following types of lung cancer cause about 90% of all lung cancer cases:

* Small cell carcinoma (also called oat cell carcinoma): usually starts in one of the larger breathing tubes, grows fairly rapidly, and is likely to be large by the time of diagnosis.

* Epidermoid carcinoma (also called squamous cell carcinoma) : usually starts in one of the larger breathing tubes and grows relatively slowly. The size of these tumors can range from very small to quite large.

* Adenocarcinoma: starts growing near the outside surface of the lung and may vary in both size and growth rate. Some slowly growing adenocarcinomas are call alveolar cell cancer.

* Large cell caracinoma: starts near the surface of the lung, grows rapidly, and is usually large when diagnosed.