There are two types of lung cancer: non-small cell and small cell.

Non-small cell lung cancer, by far the most common type, is divided into three subtypes.

• Adenocarcinoma starts in the cells that secrete substances such as mucus. Although it occurs mainly in people who have smoked, it’s also the most common kind of lung cancer in people who never smoked. It is found in the outer part of the lungs and most likely to be discovered before it has spread.

• Squamous cell carcinoma occurs in the center of the lungs in cells that line the inside of the airway and is often linked with a history of smoking.

• Large cell, or undifferentiated, lung cancer can appear anywhere in the lungs and tends to grow and spread aggressively.

Small cell lung cancer tends to grow and spread faster than non-small cell lung cancer. More treatments are available for non-small cell lung cancer than for small cell lung cancer.