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.
|Malignant tumours ('cancers')
Malignant tumours tend to grow quite quickly, and invade into nearby tissues and organs which can cause damage. The original site where a tumour first develops is called a primary tumour. Malignant tumours may also spread to other parts of the body to form 'secondary' tumours (metastases). 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.
|Local growth and damage to nearby tissues
Malignant cells multiply quickly. However, to get larger, a tumour has to develop a blood supply to obtain oxygen and nourishment for the new and dividing cells. In fact, a tumour would not grow bigger than the size of a pin head if it did not also develop a blood supply. Cancer cells make chemicals that stimulate tiny blood vessels to grow around them which branch off from the existing blood vessels. This ability for cancer cells to stimulate blood vessels to grow is called 'angiogenesis'.
Malignant cells have the ability to push through or between normal cells. So, as they divide and multiply, malignant cells invade and damage the local surrounding tissue.
|Spread to lymph channels and lymph nodes
Some malignant cells may get into local lymph channels. (The body contains a network of lymph channels which drains the fluid called lymph which bathes and surrounds the the body's cells.) The lymph channels drain lymph into lymph nodes (sometimes called lymph glands). There are many lymph nodes all over the body. A malignant cell may be carried to a lymph node and there it may become trapped. However, it may multiply and develop into a tumour. This is why lymph nodes that are near to a tumour may enlarge and contain cancerous cells.
|Spread to other areas of the body
Some malignant cells may get into a local small blood vessel (capillary). They may then get carried in the bloodstream to other parts of the body. The cells may then multiply to form 'secondary' tumours (metastases) in one or more parts of the body. These secondary tumours may then grow, invade and damage nearby tissues, and spread again.
|Why do benign tumours not spread to other areas?
Cells that make up benign tumours are different to malignant cells. Cells in benign tumours tend to be quite similar to normal cells. They do not invade local tissues. A benign tumour often grows slowly within a 'capsule' or within normal cells which surround the tumour. A benign tumour tends to look and feel smooth and regular and have a well defined edge. This is unlike a malignant tumour which may look 'craggy' and irregular, and its edges tend to be mixed up with the nearby normal cells and tissue.