A tumour is defined as an abnormal tissue growth that serves no useful function in the body. "Tumour" should thus not be readily associated with cancer until proper diagnostic procedures have been performed ...
Benign Tumours
Freckles, moles, and fatty lumps under the skin all represent benign tumours: abnormal cell growths that do not pose any dangers to surrounding tissue. They can be removed or left alone, generating only aesthetic concerns, if any. It is important to note that benign tumours, wherever they may be located, are confined to a certain area and do not impede bodily function.
Malignant Tumours
The danger of abnormal cell growth is not the mass itself but rather its ability to invade surrounding tissue and to spread to other, often distant, parts of your body. This more invasive type of cell growth is what is referred to as a cancerous, or malignant tumour. Contrary to common perception, the difference between benign and malignant growth is not clear-cut. Although truly benign tumours exist (as in the examples above) as do ones that are unquestionably cancerous, the spectrum of cancer behaviour is not simply black and white.
Crossing the Line
While there are benign tumours that predispose themselves to becoming cancerous, some tumours that are more malignant in nature progress so slowly that they never pose a threat to your health, treated or not. Generally speaking, though, the ability of a tumour to invade surrounding tissue, to grow rapidly, and to metastasize (spread) from its site of origin to distant parts of your body, is clear evidence of both malignancy and serious health concern.
