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.

How chemotherapy drugs work

Chemotherapy drugs can stop cancer cells dividing and reproducing themselves. As the drugs are carried in the blood, they can reach cancer cells anywhere in the body. They are also taken up by some healthy cells. Healthy cells can repair the damage caused by chemotherapy, but cancer cells cannot and so they eventually die.

Different chemotherapy drugs damage cancer cells in different ways. If a combination of drugs is used, each drug is chosen because of its different effects.

Unfortunately, as the chemotherapy drugs can also affect some of the healthy cells in your body, they can cause unpleasant side effects. However, damage to the healthy cells is usually temporary and most side effects will disappear once the treatment is over.

Healthy cells in certain parts of the body are especially sensitive to chemotherapy drugs; these parts of the body include:

• the bone marrow (which makes blood cells)
• the hair follicles
• the lining of the mouth
• the digestive system.

Chemotherapy is usually given as a series of sessions of treatment. Each session is followed by a rest period. The session of chemotherapy and the rest period is known as a cycle of treatment. A series of cycles makes up a course of treatment.

Each session of chemotherapy destroys more of the cancer cells, and the rest period allows the normal cells and tissues to recover.

Why chemotherapy is given

• With some types of cancer, chemotherapy is likely to destroy all the cancer cells and cure the disease.
• Chemotherapy may also be given after surgery or radiotherapy to destroy any cancer cells that remain.
• Chemotherapy may be given to shrink a cancer before another treatment such as surgery.
• It can also be given to shrink and control a cancer to help reduce symptoms and prolong life. This is known as palliative chemotherapy.

When chemotherapy is used

Before an operation

Chemotherapy can be used before an operation (this is known as neo-adjuvant or primary chemotherapy) to shrink a cancer that is too large – or too attached to surrounding healthy tissue – to be removed easily during an operation. This can make removing the cancer easier during a later operation.

After an operation

Chemotherapy can be given after an operation (this is known as adjuvant chemotherapy) when all the visible cancer has been removed but there is a risk that some cancer cells, which are too small to be seen, may have been left behind. The aim is to destroy these cancer cells.

Chemotherapy may also be given if a cancer cannot be completely removed during an operation. In this situation chemotherapy may not be able to cure the cancer but may shrink it and so reduce symptoms.

During radiotherapy

Sometimes chemotherapy is given at the same time as radiotherapy. This is known as chemoradiotherapy or chemo-radiation.

In advanced cancer

Where cancer has spread into surrounding tissue or other parts of the body (advanced cancer), chemotherapy can sometimes be given with the aim of getting rid of all the cancer and curing it. More commonly however, chemotherapy is given to people in this situation to shrink and control the cancer, to try to extend life and control any symptoms that may occur.

High-dose chemotherapy with bone marrow transplant or stem cell support

For some types of cancer, high-dose chemotherapy is given. This is usually done after initial chemotherapy has got rid of the cancer cells but there is a high risk of the cancer coming back. High doses of chemotherapy would normally destroy the bone marrow – which makes the blood cells – so the bone marrow has to be replaced after the chemotherapy has been given. This is done using stem cells which have been collected from the bone marrow or blood. The stem cells are collected before the high-dose treatment, either from the patient, or from someone else (a donor) whose cells are a good match. They settle in the bone marrow and develop into the different blood cells. This type of treatment is only used in a few types of cancer.

Our booklet on stem cell and bone marrow transplants discusses this treatment in detail.