大象传媒

Cancer

Cells grow then divide by only when we need new ones. This is when we're growing or need to replace old or damaged cells.

When a cell becomes , it begins to grow and divide uncontrollably because they do not respond to regulatory signals. New cells are produced even if the body does not need them. A group of cancerous cells produces a growth called a .

Types of tumour

Tumours are of two types called and :

Type of tumourCharacteristics
BenignGrow slowly. Usually grow within a membrane, so can easily be removed. Do not invade other parts of the body.
MalignantGrow quickly. Invade neighbouring tissues and can spread to other parts of the body in the bloodstream. As the tumour grows, cancer cells may fail to attach to each other, spreading through the body where they may form secondary tumours. This process is called metastasis.
Type of tumourBenign
CharacteristicsGrow slowly. Usually grow within a membrane, so can easily be removed. Do not invade other parts of the body.
Type of tumourMalignant
CharacteristicsGrow quickly. Invade neighbouring tissues and can spread to other parts of the body in the bloodstream. As the tumour grows, cancer cells may fail to attach to each other, spreading through the body where they may form secondary tumours. This process is called metastasis.

The diagram shows how cancer cells can invade surrounding tissue:

Image gallerySkip image gallerySlide 1 of 2, This shows how cancer cells can invade surrounding tissue., Growth of a malignant tumour by mitosis

Cancer cells are undifferentiated 鈥 they do not carry out their normal function.

At some point, secondary tumours may develop.

Image gallerySkip image gallerySlide 1 of 5, Diagram of how the tumour secretes chemicals, The spread of a tumour by metastasis