What is lung cancer?

Lung cancer is cancer of some of the cells in part of your lung, usually beginning in the lining of the bronchus (airways) or bronchioles (small tubes). Lung cancer is the most common cause of death from cancer for New Zealand men, and the second most common for women. Smoking is the main cause of lung cancer.

How the lungs work

The chest cavity ('thorax') is the area enclosed by your ribs, from below your neck and shoulders. Its base is the diaphragm, a wide, thin dome of muscle a little above your waist. Below the diaphragm is the abdomen.

Most of the chest cavity is filled with the two large, spongy lungs. The lungs are roughly cone-shaped, and are made up of sections or lobes. The left lung has two (upper and lower lobes) and the right lung has three (upper, middle and lower lobes).

Between the lungs is the mediastinum (the name of the area that contains the heart and large blood vessels), the oesophagus (the tube that carries food from mouth to stomach), many glands called lymph nodes, and the trachea (windpipe). 

The windpipe divides into two airways. These are called the right main bronchus and left main bronchus. One goes to each lung. Within the lungs, the bronchi (the plural of bronchus) divide into smaller tubes called the secondary bronchi. Each secondary bronchus divides into smaller tubes called bronchioles. Each bronchiole ends up in a tiny, bubble-like air sac. It is these air sacs (alveoli) that make the lungs spongy.

When we breathe in, air goes through the nose or mouth, into the throat and down the windpipe and bronchi until it reaches the alveoli. Blood flows between the thin walls next to air sacs in the alveoli.

This allows oxygen to move from the air into the blood, and carbon dioxide (a waste product) to move from blood to air to be breathed out.

The pleura help protect the lungs

The pleura are two fibrous sheets of tissue that cover the lungs and help to protect them. Doctors usually call these the lining of the lungs, although for non medical people this can be a bit confusing as they are on the outside of the lungs. The pleura are also sometimes called the pleural membranes. They are about the thickness of plastic food wrap. The inner (visceral) layer is attached to the lungs and the outer (parietal) layer lines the chest wall and diaphragm.

The gap between the pleura is called the pleural space or cavity. The pleura produce a lubricating fluid that fills the gap between them. As we breathe this helps the lungs to move smoothly in the chest when they are inflating and deflating.

Two main types of lung cancer

There are different types of lung cancer, and the two main types are 'small cell lung cancer' and 'non-small cell lung cancer'.

Small cell lung cancer

A medical term for a cancer that arises in the cells lining an organ, is a 'carcinoma'. Small cell lung cancer (also called 'oat cell carcinomas' because of the cell shape), account for around 15% of lung cancers. This type of lung cancer is strongly associated with cigarette smoking. Unfortunately, it grows rapidly, spreads early and causes few early symptoms. Often it has already spread (metastasised) at the time of diagnosis so surgery is not helpful.

Non-small cell lung cancer

Non-small cell carcinomas include squamous cell carcinoma and adenocarcinoma. Also in this group are rare cancers such as large cell carcinoma and bronchiolo-alveolar cell carcinoma.

The most common types of lung cancers affect the cells that line the main bronchi. As these tumours enlarge they can block off the bronchi and reduce the air flow into parts of the lung. They commonly spread into the local lymph nodes and occasionally may affect the chest wall, causing pain. 

Squamous cell carcinoma has a lower rate of metastasis (spread to other parts of the body) than other types of lung cancer. If it is discovered early, it may result in a better prognosis following treatment. Adenocarcinoma is a cancer of the glandular cells of the lung.

Mesothelioma

Mesothelioma is not, strictly speaking, a lung cancer. It is a rare cancer of the pleural membranes on the surface of the lungs and is strongly related to asbestos exposure.

Causes of lung cancer

Smoking is the single main avoidable cause of lung cancer. It is not known why one smoker develops lung cancer and another does not. Up to 90% of lung cancer is caused by smoking.

Lung cancer occurs most often in adults between the ages of 40 and 70 who have smoked cigarettes for at least 20 years. They are also likely to have started smoking as teenagers.

Second-hand smoking (passive smoking) may also cause lung cancer. However, as with many cancers, we do not know the cause in all cases. How to quit smoking.

Occupational exposure to asbestos is associated with an increased risk of asbestosis, mesothelioma and lung cancer. For people with asbestosis, their risk of developing lung cancer is doubled. If the person also smokes, then the risk is increased.

Other occupational exposures that possibly are associated with lung cancer include contact with the processing of steel, nickel, chrome and coal gas. Exposure to radiation causes an increased risk of all cancers, including lung cancer.

Miners of uranium, fluorspar and haematite may be exposed to radiation by breathing air contaminated with radon gas.

How many people get lung cancer?

The latest provisional data (data that have yet to be finalised) available from the Ministry of Health record 1713 new cases of trachea, bronchus and lung cancer in New Zealand in 2008.

Twice as many men as women die from lung cancer, but the incidence is increasing among women. There is some evidence that women may be particularly sensitive to the cancer-causing effects of cigarette smoke.

Related topics

Also see What is cancer? and Lung cancer diagnosis; and Lung cancer treatment

What does that term mean? See Cancer glossary

Original material provided by the Cancer Society of New Zealand, 2010. Edited by everybody, July 2010.