There are 2 main types of lung cancer, which are named for the size of the cancer cells seen under a microscope: small cell lung cancer and non–small cell lung cancer. Around 85–90% of lung cancers are non–small cell cancers.^[1]

The 3 main subtypes of non–small cell lung cancer are:^{[2],[3],[4],[5]}

• adenocarcinoma – the commonest form of non–small cell lung cancer, which starts in the mucus-secreting cells in the deeper part of the lungs. This is the most common form of cancer in non-smokers, and is also more likely to occur in younger people than other types of lung cancer
• squamous cell (epidermoid) carcinoma, which starts in the cells lining the airways of the lungs, usually close to a main airway
• large cell (undifferentiated) carcinoma, which may begin in several types of cells. Small cell lung cancer tends to grow and spread quickly. It has usually spread to other parts of the body before it is detected.

There are other types of lung cancer, but they are all less common.

Cancers that start in other organs (such as breast cancer) and metastasise (spread) to the lungs are not lung cancers. They are treated according to where they started in the body.