Types of Cancer

What are the different types of cancer?

There are more than 100 different types of cancer. Each type is classified by the type of cell the cancer originates from. For example, a breast cell, a lung cell, etc. Each type of cancer generally falls into one of three categories:

• Carcinomas are cancers that arise from cells which line a body surface, or the lining of a gland - for example, the skin, or the lining of the gut, mouth, neck of the womb (cervix), airways, etc.
• Sarcomas are cancers that arise from cells which make up the connective tissues such as bones or muscles. For example, an osteosarcoma is a cancer of bone tissue.
• Leukaemias and lymphomas are cancers of cells in bone marrow and lymph glands. For example, leukaemia is a cancer of cells that make white blood cells.

What are tumours?

A tumour is a lump or growth of tissue made up from abnormal cells. Tumours are divided into two types: benign and malignant.

Non-cancerous (benign) tumours

These may form in various parts of the body. Benign tumours grow slowly and do not spread or invade other tissues. They are not cancerous and are not usually life-threatening. They often do no harm if they are left alone. However, some benign tumours can cause problems. For example, some grow quite large and may cause local pressure symptoms, or look unsightly. Also, some benign tumours that arise from cells in hormone glands can make too much hormone, which can cause unwanted effects.

Cancerous (malignant) tumours

Malignant tumours tend to grow quite quickly, and invade into nearby tissues and organs, which can cause damage. Tumours normally develop in one original site - the primary tumour. Malignant tumours may also spread to other parts of the body to form secondary tumours (metastases). This happens if some cells break off from the primary tumour and are carried in the bloodstream or lymph channels to other parts of the body. These secondary tumours may then grow, invade and damage nearby tissues, and spread again.

Note: not all cancers form solid tumours. For example, in cancer of the blood cells (leukaemia) many abnormal blood cells are made in the bone marrow and circulate in the bloodstream.

What is carcinoma in situ?

A carcinoma in situ is the very early stage of a cancer when the abnormal cancer cells are confined to their original site. At this stage no tumour has grown and no cancer cells have spread. It may be that many cancers remain at this dormant stage for months, or even years, before they start to grow and spread into a proper cancer. This may be because the cells of the carcinoma in situ do not have the ability to stimulate new blood vessels. If they cannot stimulate new blood vessels to grow then the cancer itself cannot grow or spread.

It is thought that one or more of the cells in a carcinoma in situ may then mutate after some time (some genes may be altered). This then gives them the ability to make chemicals to stimulate new blood vessels. The cancer then grows and spreads as described above.

A carcinoma in situ contains only a small number of cells and is usually too small to be detected by scans or X-rays. However, some screening tests may detect a carcinoma in situ. For example, some cells from an abnormal cervical screening test, looked at under the microscope, may show carcinoma in situ. These cells can then be destroyed by treatment which prevents cancer from developing. Sometimes a small sample (a biopsy) taken from a part of the body may show a carcinoma in situ.