A removed section of a colon with colon cancer. In the middle, the dark-red part is a tumor, as shown by the uncontrollable growth of cells.

Tasmanian devil with a tumour

A neoplasm (or neoplasm) is tissue that is growing where it should not be. If they become a mass, they become a tumour. Tumours are either malignant (harmful) or benign (safe). Cancer, for example is malignant and sometimes spreads to other places on the body. Some tumours have a cause that makes them grow. For some tumours no cause is known. A tumour usually forms as a lump or mass.