Cancer begins in cells, the building blocks that make up tissues. Tissues make up the organs of the body.
Normally, cells grow and divide to form new cells as the body needs them. When cells grow old, they die, and new cells take their place.
Sometimes this orderly process goes wrong. New cells form when the body does not need them, and old cells do not die when they should. These extra cells can form a mass of tissue called a growth or tumour. Not all tumours are cancer.
Tumours can be benign or malignant:
Benign tumours are not cancer:
- They are rarely life threatening.
- Usually, benign tumours can be removed, and they seldom grow back.
- Cells from benign tumours do not spread to tissues around them or to other parts of the body.
Malignant tumours are cancer:
- They are generally more serious and may be life threatening.
- Malignant tumours usually can be removed, but they can grow back.
- Cells from malignant tumours can invade and damage nearby tissues and organs. Also, cancer cells can break away from a malignant tumour and enter the bloodstream or lymphatic system. That is how cancer cells spread from the original cancer (the primary tumour) to form new tumours in other organs. The spread of cancer is called metastasis. Different types of cancer tend to spread to different parts of the body.
- (US National Cancer Institute, November 2007)