Lung cancer is the leading cause of cancer deaths in both women and men in the United States and throughout the world. Lung cancer is the number one cause of cancer deaths in men and has surpassed breast cancer as the leading cause of cancer deaths in women. In the United States in 2004, 160,440 people were projected to die from lung cancer compared with a projected 127,210 deaths from colorectal, breast, and prostate cancer combined. Only about 14% of all people who develop lung cancer survive for 5 years.
Cancer occurs when normal cells undergo a transformation that causes them to grow and multiply without the normal controls. The cells form a mass or tumor that differs from the surrounding tissues from which it arises. Tumors are dangerous because they take oxygen, nutrients, and space from healthy cells.
Most lung tumors are malignant. This means that they invade and destroy the healthy tissues around them.
The tumors can also spread to nearby lymph nodes or through the bloodstream to other organs. This process is called metastasis.
When lung cancer metastasizes, the tumor in the lung is considered the primary tumor, and the tumors in other parts of the body are called secondary tumors or metastatic tumors.
Some lung tumors are metastatic from cancers elsewhere in the body. The lungs are a common site for metastasis. Lung cancers are usually divided into 2 groups that account for about 95% of all cases.
The division is based on the type of cells that make up the cancer.
The 2 types of lung cancer are classified based on the cell size of the tumor. They are called small cell lung cancer (SCLC) and non–small cell lung cancer (NSCLC). NSCLC includes several more types of tumors.
SCLCs are less common, but they grow more quickly and are more likely to metastasize than NSCLCs. Often, SCLCs have already spread to other parts of the body when the disease is diagnosed.
About 5% of lung cancers are of rare cell types, such as carcinoid tumor, lymphoma, or metastatic (cancers from other parts of the body that spread to the lungs).
The specific types of primary lung cancers are as follows:
Adenocarcinoma (an NSCLC) is the most common type of lung cancer, making up 30-40% of all cases. A subtype of adenocarcinoma is called bronchoalveolar cell carcinoma, which creates a pneumonialike appearance on chest x-ray films.
Squamous cell carcinoma (an NSCLC) is the second most common type of lung cancer, making up about 30% of all lung cancers.
Large cell cancer makes up 10% of all cases.
SCLC makes up 20% of all cases.