The biology of cell death in tumours.

The principal objective of this article is to present evidence for the numerical and biological importance of cell death in tumour growth and regression. Much of this death has the morphology of apoptosis, a process observed elsewhere in biology in a variety of circumstances. Recent studies on the mechanism of apoptosis in non-neoplastic cells suggest that a relatively small number of specific intracellular changes are involved. Two of these are described: endonuclease activation within the nucleus, which coincides with the characteristic morphological changes there, and altered expression of surface carbohydrates, which may be responsible for the swift recognition and phagocytosis of apoptotic cells. It seems probable that similar events occur during the apoptosis of tumour cells. Further knowledge of the control of these endogenous mechanisms for effecting cell death could lead to powerful new means of controlling the growth of tumours.