Last reviewed 01/2018

A tumour is strictly an abnormal swelling. The term was originally applied to inflammatory masses. However, modern usage implies that of a new growth - neoplasm - most commonly in the context of cancer.

A tumour grows without the control of normal physiological regulatory mechanisms. This results in an abnormal body of tissue excessively large or uncoordinated in its growth relative to its tissue of origin. Tumours are rigorously defined as being benign or malignant. Benign tumours only show local invasion whereas malignant types are capable of metastasis. In practice, there is a spectrum of characteristics which one tumour may traverse during its dysfunctional lifespan.

Oncology is the study of tumours.