Give four differences between benign and malignant tumours.

Benign tumour	Malignant tumour
They are not cancerous and do not invade nearby cells. They have clear boundaries.	They are cancerous, do not have clear boundaries and invade nearby cells.
They are generally not dangerous (except when present in the brain).	They are generally dangerous as they may metastasize.
They do not recur on being removed.	They may recur even after being removed.