Several types of lung cancer exist, but all can be divided into two main categories: small cell lung cancer (SCLC) and non-small cell lung cancer (NSCLC). The category is determined by the cells within the lungs that are affected. Although nonsmokers can develop lung cancer, the vast majority-almost 90 percent-of all lung cancer cases can be traced to active smoking or to secondhand smoke. Asbestos and exposure to radon are also common causes.
Non-small cell lung cancer
NSCLC is the most common type of lung cancer. About 80 to 85 percent of all lung cancers diagnosed are of this type. The name is derived from the appearance of the affected cells when they are examined under a microscope. NSCLC is divided into four different types, each based the location of the cancer within the lungs.
Adenocarcinoma affects glands in the lungs that create mucus. These cancers occur more often at the lungs' outer edges, closer to the skin. Although this can make it easier to collect tissue for a biopsy, it also means that this type of cancer is more likely to spread into other areas, such as the lymph nodes. This type of lung cancer is also found in nonsmokers, especially women and Asians. About 30 to 40 percent of lung cancer cases are of this type.
Squamous cell carcinoma
Squamous cell carcinoma is found in the bronchial tube lining and is almost always caused by exposure to cigarette smoke. These cancers are most commonly located toward the center of the chest and can spread into the lymph nodes. Its presence in the bronchial tubes leads to early symptoms, such as a nagging cough that produces blood, making it easier to diagnose at early stages. About one-third of lung cancer diagnoses are squamous cell carcinomas.
Large cell carcinoma
These cancers do not fit into the other lung cancer categories and affect different types of cells on or near the lung surface. They can grow quickly and often spread to the lymph nodes and elsewhere in the body.
Small cell lung cancer
This type of lung cancer is less common and more aggressive than NSCLC. It grows on the outside of the bronchial tubes. Ninety-nine percent of these cancers can be directly attributed to smoking. SCLC is often not discovered until it has metastasized, because it grows very quickly. Although SCLC responds well to chemotherapy and radiation, its fast growth and tendency to metastasize means prognosis is often poor.