Types of lung cancer

Cancer that starts in the lung is called primary lung cancer. There are several different types and these are divided into two main groups

• Small cell lung cancer
• Non small cell lung cancer

Small cell lung cancer

About 18 out of every 100 lung cancers diagnosed are this type. Small cell lung cancer is called this because under the microscope the cancer cells look small and are mostly filled with the nucleus (the control centre of cells). It is also called oat cell cancer. This type of cancer is usually caused by smoking. It is very rare for someone who has never smoked to develop it. Small cell lung cancer often spreads quite early on and so your doctors may recommend chemotherapy treatment rather than surgery.

Non small cell lung cancer

There are three common types of non small cell lung cancer. These are grouped together because they behave in a similar way and respond to treatment in a different way to small cell lung cancer. They make up about 78 out of 100 lung cancers in the UK. The three types are

• Squamous cell carcinoma
• Adenocarcinoma
• Large cell carcinoma

Occasionally it is not possible to work out which type of non small cell lung cancer you have. It may not be possible to tell if only a few cells are taken during a biopsy. It can also be difficult if the cells are very undeveloped. Undeveloped cancer cells are known as undifferentiated cells. So your doctor will say that you have undifferentiated non small cell lung cancer. This will not usually make any difference to your treatment, because most non small cell lung cancers are treated in the same way.

Squamous cell cancer

Squamous cell cancer is the most common type of lung cancer. It develops from the cells that line the airways and it is often found near the centre of the lung in one of the main airways (the left or right bronchus). This type of cancer is often due to smoking. The number of people developing squamous cell lung cancer is going down in the UK.

Adenocarcinoma

Adenocarcinoma also develops from the cells that line the airways. But it develops from a particular type of cell that produces mucus (phlegm). It is often found in the outer areas of the lungs. The number of people developing adenocarcinoma is increasing and it may soon become more common in the UK than squamous cell lung cancer.

Large cell carcinoma

Large cell lung cancer is called this because the cells look large and rounded under a microscope. This type of lung cancer tends to grow quite quickly.

Cancer that has spread from somewhere else in the body is called secondary cancer. Quite a few different types of cancer can spread to the lung, including breast cancer and bowel cancer. If you are diagnosed with lung cancer and have already had another type of cancer, check with your doctor whether the cancer started in the lung or has spread into the lung.

If you have secondary cancer you need to look at the section about where the cancer started. For example, if you had breast cancer that has spread to the lungs, then you need to look at the section about breast cancer. It is important to know which type of cancer you have so that you can find the right information. The choice of cancer treatment depends on where the cancer started. When cancer spreads to the lung from the breast, the cells are breast cancer cells, not lung cancer cells. So they respond to breast cancer treatments. And cancer that has spread from the bowel should respond to bowel cancer treatments.

Mesothelioma is a rare type of cancer that affects the covering of the lung (the pleura). It is often caused by exposure to asbestos. It is very different to lung cancer. We have a whole section about mesothelioma.