Introduction

This booklet is for you if you have or someone close to you has cancer of the lung.

If you are a patient your doctor or nurse may wish to go through the booklet with you and mark sections that are particularly important for you.

The lungs

When you breathe in, air passes from your nose or mouth through the windpipe (trachea), which divides into two tubes (airways), one going to each lung. These are known as the right and left bronchus and they divide to form smaller tubes called bronchioles, which carry air through the lungs. At the end of the bronchioles are millions of tiny air sacs called alveoli. In the alveoli, oxygen is absorbed from the air we breathe in and passes into the bloodstream to be circulated around the body.

Carbon dioxide is a waste gas that must be removed from the body. It passes from the bloodstream into the alveoli and is then breathed out by the lungs.

The right lung has three main areas (known as lobes) and the left lung has two.

Many lung cancers start in the cells lining the bronchi and are called carcinomas of the bronchus.

Figure: The lungs and surrounding structures

What is cancer?

The organs and tissues of the body are made up of tiny building blocks called cells. Cancer is a disease of these cells.

Cells in different parts of the body may look and work differently but most reproduce themselves in the same way. Cells are constantly becoming old and dying, and new cells are produced to replace them. Normally, cells divide in an orderly and controlled manner. If for some reason the process gets out of control, the cells carry on dividing, developing into a lump which is called a tumour.

Tumours can be either benign or malignant. Cancer is the name given to a malignant tumour. Doctors can tell if a tumour is benign or malignant by examining a small sample of cells under a microscope. This is called a biopsy.

In a benign tumour the cells do not spread to other parts of the body and so are not cancerous. However, if they continue to grow at the original site, they may cause a problem by pressing on the surrounding organs.

A malignant tumour consists of cancer cells that have the ability to spread beyond the original area. If the tumour is left untreated, it may spread into and destroy surrounding tissue. Sometimes cells break away from the original (primary) cancer. They may spread to other organs in the body through the bloodstream or lymphatic system.

The lymphatic system is part of the immune system - the body's natural defence against infection and disease. It is a complex system made up of organs, such as bone marrow, the thymus, the spleen, and lymph nodes. The lymph nodes (or glands) throughout the body are connected by a network of tiny lymphatic ducts.

When the cancer cells reach a new area they may go on dividing and form a new tumour. This is known as a secondary cancer or metastasis. Even when the cancer spreads somewhere else in the body, it is still referred to as the site where it was originated, and is still named after the part of the body where it started. For example, if lung cancer spreads to bones, it is still termed as lung cancer and not bone cancer. In that case, it may be said that the person has "lung cancer with bone metastases”.

It is important to realise that cancer is not a single disease with a single type of treatment. There are more than 200 different kinds of cancer, each with its own name and treatment.

Types of cancer

Carcinomas

The majority of cancers, about 85% (85 in a 100), are carcinomas. They start in the epithelium, which is the covering (or lining) of organs and of the body (the skin). The common forms of breast, lung, prostate and bowel cancer are all carcinomas.

Carcinomas are named after the type of epithelial cell that they started in and the part of the body that is affected. There are four different types of epithelial cells:

• squamous cells - that line different parts of the body, such as the mouth, gullet (oesophagus), and the airways
• adeno cells - form the lining of all the glands in the body and can be found in organs such as the stomach, ovaries, kidneys and prostate
• transitional cells - are only found in the lining of the bladder and parts of the urinary system
• basal cells - that are found in one of the layers of the skin.

A cancer that starts in squamous cells is called a squamous cell carcinoma. A cancer that starts in glandular cells is called an adenocarcinoma. Cancers that start in transitional cells are transitional cell carcinomas, and those that start in basal cells are basal cell carcinomas.

Leukaemias and lymphomas

These occur in the tissues where white blood cells (which fight infection in the body) are formed, i.e. the bone marrow and lymphatic system. Leukaemia and lymphoma are quite rare and make up about 6.5% (6.5 in 100) of all cancers.

Sarcomas

Sarcomas are very rare. They are a group of cancers that form in the connective or supportive tissues of the body such as muscle, bone and fatty tissue. They account for less than 1% (1 in 100) of cancers.

Sarcomas are split into two main types:

• bone sarcomas - that are found in the bones
• soft tissue sarcomas - that develop in the other supportive tissues of the body.

Others forms of cancer

Brain tumours and other very rare forms of cancer make up the remainder of cancers.

Types of lung cancer

Primary lung cancer

Each year over 38,000 people in the UK are diagnosed with lung cancer.

There are two main types of primary lung cancer, which behave and respond to treatment quite differently. They are:

non-small cell lung cancer (NSCLC)
small cell lung cancer (SCLC).

About 1 in 5 lung cancers are small cell; the rest are non-small cell.

Non-small cell lung cancer

There are three main types of non-small cell lung cancer. Sometimes it's not possible to tell which type someone has. This is because when the cells are looked at under a microscope they are not developed enough. The three types are:

Squamous cell carcinoma: This is the most common type of lung cancer. It develops in the cells which line the airways. This type of lung cancer is often caused by smoking.

Adenocarcinoma: This develops from the cells which produce mucus (phlegm) in the lining of the airways. This type of cancer is becoming more common.

Large cell carcinoma: This gets its name from the large, rounded cells that are seen when they are examined under the microscope. It is sometimes known as undifferentiated carcinoma.

Mesothelioma

A less common type of cancer that can affect the covering of the lungs is called mesothelioma. It is a cancer of the membrane which covers the surface of the lungs and lines the inside of the chest. It often occurs in people who have been exposed to asbestos.

Mesothelioma is discussed in its own booklet.