The emergence of cancer cells within the body may not be a rare or
unusual event at all. Of the trillions of normal cells found in the body,
several hundred per day may be undergoing malignant degeneration in response to
the cancer-promoting stimuli. The immune system may possibly play a significant
role in halting the growth of these cells and preventing the development of
The concept of immune surveillance was initially put for-ward by
Ehrlich, and later on modified by Thomas and Burnet. Ehrlich first suggested
that though cancer cells frequently arise in the body, they are recognized as
foreign and eliminated. Later, Burnet postulated the immunosurveillance theory.
He suggested that the immune system routinely patrols the cells of the body and
upon recognition of a cell or a group of cells that has become cancerous
attempts to destroy them, thus pre-venting the growth of some tumors.