When a person is growing or replacing old and damaged cells, new cells are produced by mitosis.
Sometimes, cells begin to divide uncontrollably. New cells are produced – even if the body does not need them. This produces a growth called a tumour.
|Type of tumour||Characteristics|
|Benign||Normally grow slowly|
|Benign||Usually grow within a membrane, so can easily be removed and in most cases do not grow back|
|Benign||Do not spread to other parts of the body|
|Benign||Can still be life-threatening if they cause damage to an organ|
|Malignant||Normally grow quickly|
|Malignant||Can spread to other parts of the body in the bloodstream|
|Malignant||As the tumour grows, cancer cells detach and can form secondary tumours in other parts of the body - this is called metastasis|
The diagrams shows how cancer cells can invade surrounding tissue:
Development of a tumour
Carcinogens cause cancer by damaging DNA. Carcinogens increase the chance that mutations will occur. A single mutation will not cause cancer – several are required. For this reason, we are more likely to develop cancer as we get older. There are several risk factors for various types of cancers.
There are genetic risk factors that increase the likelihood of developing some cancers. For example, inheriting a mutation in the BRCA1 gene can increase a person's risk of developing breast cancer.