When the tumor grows on or near a surface, it may project from this and be attached by a narrow band only; in the interior of the body it may be irregular in outline, round or lobular, the shape being influenced by many factors.

Tumors like the tissues of the normal body are nourished by the blood and contain blood vessels often in great numbers.
A tumor arises by the cells of a part of the body beginning to grow and taking on the characteristics of a tumor.

Its growth is independent, the cells of the adjoining tissue taking no part in it.
The tissue in the vicinity of the tumor is partly pushed aside by the mass, or the tumor grows into it and the tissue disappears as the tumor advances.

The destruction of the surrounding tissue is brought about partly by the pressure which the tumor exerts, partly by the compression of the blood vessels or the blood supply of the organs is diverted to the tumor.
The characteristics of a tumor are due to the cells which it contains (Fig 14).

These often become separated from the main mass and are carried by the blood into other parts of the body, where they grow and form tumors similar in character to the parent tumor.