There are two major types of lung cancer. They are Non-small cell lung cancer (NSCLC) and small cell lung cancer (SCLC) or oat cell cancer. The classification of the lung cancer is based upon the microscopic appearance (i.e. cell size) of the tumor cells. Each type of lung cancer grows and spreads in different ways, and is treated differently. If the cancer has features of both types, it is called mixed small cell/large cell cancer.

Non-small cell lung cancer is more common than SCLC and it generally grows and spreads more slowly. There are three main types of NSCLC. They are :
1. Squamous cell carcinoma or epidermoid carcinoma usually starts in the large bronchi and very often stays in the central chest area, without spreading, for longer periods of time than other lung cancers.
2. Adenocarcinoma are found along the outer or peripheral areas of the lungs and under the lining of the bronchi. Bronchioloalveolar carcinoma, a sub type of adenocarcinoma develops around scars on the outer edges of the lungs.
3. Large cell carcinoma, can be found in any part of the lung and tends to grow and spread quickly. It is also known as undifferentiated carcinomas.

SCLC are almost related with smoking and grows more quickly and form large tumors that can spread widely through the body. They often starts in the bronchi near the center of the chest.

Other tumors found in the lungs are :

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Carcinoid tumor which arise from glands near the bronchi. This slow-growing tumor is usually cured by surgery.
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Lymphoma or metastatic
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Mesothelioma, a less common type is found in people who have been exposed to asbestos. It is a cancer of the membrane which covers the surface of the lungs and lines the inside of the chest. Exposure to asbestos particles in the air increases the risk of developing malignant mesothelioma.