Tumours
A tumour is a mass of abnormal cells produced as cells divide. Tumours can be classified as benign or malignant according to their behaviour.
Both types can cause damage. A growing mass may interfere with the function of the organ containing it, cause an obstruction or exert pressure on nearby tissues.
| Characteristic | Benign tumour | Malignant tumour |
|---|---|---|
| Cancerous? | No | Yes |
| Growth | Generally slow | Can grow rapidly |
| Invasion | Does not invade neighbouring tissues | Invades and damages surrounding tissues |
| Metastasis | Does not metastasise | Cells can spread and establish secondary tumours |
| After removal | Usually does not grow back | May recur |
How malignant tumours spread
Cells in a malignant tumour can release chemicals that stimulate formation of new blood vessels. These vessels supply the tumour with oxygen, nutrients and growth factors that support its continued development.
Some malignant cells detach from the original tumour and enter the bloodstream or lymphatic system. They can then travel elsewhere in the body and establish a secondary tumour. This spread is called metastasis.
- An abnormal cell escapes normal controls over cell division.
- Repeated mitosis produces an enlarging mass of cells.
- The tumour gains a blood supply that supports further growth.
- Malignant cells invade surrounding tissues.
- Some cells enter blood or lymph and may establish secondary tumours elsewhere.
Exam Tip: The defining distinction is not simply growth rate. For a malignant tumour, include invasion of surrounding tissue and the ability to metastasise.