Cellular Mortality, Growth Regulation, and the Phenomenon of Cancerous Transformation
Over the past few decades a huge research effort has been devoted to understanding the mechanisms of cancerous transformation. This effort has led to recognition of the fact that the unrestricted growth of most cancer cells is caused by release of normal cells within the body from the regulatory constraints imposed upon them. An understanding of cancerous transformation therefore leads to knowledge of the events controlling normal cell proliferation. In this chapter we shall first discuss the possible evolutionary origins of differentiated animal cells, both somatic (tissue) cells and germ (reproductive) cells. Subsequently, we shall consider the events that occur when normal cells become cancerous. It will become apparent that two distinct events frequently (but not always) accompany the transformation process: loss of sensitivity to growth regulation, and loss of the constraints of cellular mortality. Further, these two events are clearly distinct from each other, as well as from the genetic events that determine expression of the differentiated state. Although the phenomenon of cell mortality sometimes referred to as programmed cell death is presently poorly understood, it seems to have evolved as the terminal step in a sequence of irreversible differentiation events.
KeywordsMigration Lymphoma Tyrosine Leukemia Recombination
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