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.

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.

What is breast cancer?

The organs and tissues of the body are made up of tiny building blocks called cells. Cancer is a disease of these cells. It is important to realise that cancer is not just one disease with a single cause and a single type of treatment. There are more than 200 different kinds of cancer, each with its own name and treatment.

A cancer that starts in the breast is known as a primary breast cancer.

Treatment for breast cancer will get rid of the cancer for many women and the cancer may not come back, so the cancer is cured.

Local recurrence

In some women, treatment for breast cancer does not remove all the cancer cells. These cells may then grow in the breast or scars – sometimes many years later. This is known as local recurrence. The cancer cells may grow into a lump in the skin of the breast over where the cancer was originally removed, or in the operation scar. Sometimes the breast cancer may re-grow in the breast tissue left after a lumpectomy.

Secondary breast cancer

In some women, cancer cells break away from the primary breast cancer and spread to other parts of the body in the bloodstream or lymphatic system (see diagram below). The cells may lie dormant (inactive) for years before they begin to grow again.

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 (lymph glands). The lymph nodes throughout the body are connected by a network of tiny lymphatic ducts.

Some time after breast cancer treatment, if cancer cells have broken away and spread to other organs of the body they may begin to grow and cause symptoms. This is known as secondary breast cancer.

Secondary cancers are also called metastases, so another name for secondary breast cancer is metastatic breast cancer. The most common places that breast cancer cells spread to are the bone, liver, lung or brain. Secondary breast cancer can also affect the lymph glands. It is most likely to affect the lymph nodes in the armpits or the lower part of the neck.

Breast cancer cells do not usually spread to many places in the body at once. Although it is possible for secondary breast cancer to affect more than one place at a time, it more commonly affects just one or two parts of the body.

Each woman's situation is individually assessed and the appropriate treatment given depending on where the breast cancer has spread to. A woman with secondary breast cancer affecting the bones will have different symptoms and may need different treatment from a woman with secondary breast cancer affecting the liver.