Cells grow then divide by mitosis only when we need new ones. This is when we're growing or need to replace old or damaged cells.
|Type of tumour||Characteristics|
|Benign||Grow slowly. Usually grow within a membrane, so can easily be removed. Do not invade other parts of the body.|
|Malignant||Grow quickly. Invade neighbouring tissues and can spread to other parts of the body in the bloodstream. As the tumour grows, cancer cells detach and can form secondary tumours in other parts of the body. This process is called metastasis.|
The diagram shows how cancer cells can invade surrounding tissue:
Cancer cells are undifferentiated – they do not carry out their normal function.
At some point, secondary tumours may develop.
There are genetic factors that increase the likelihood of developing some cancers. Chemicals and other agents that can cause cancer are called carcinogens.
Carcinogens cause cancer by damaging DNA. Carcinogens cause mutations to occur. A single mutation will not cause cancer. Several are required for this to occur. For this reason, we are more likely to develop cancer as we get older.
Something that increases the likelihood of developing a disease is called a risk factor. There are several risk factors for various types of cancers including:
There are also genetic risk factors for some cancers.