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| Modern Genetic Analysis Chapter 15. Regulation of Cell Number: Normal and Cancer Cells Summary Higher eukaryotic cells have evolved mechanisms that control their structure and their ability to proliferate. These controls are all highly integrated and depend on the continual evaluation of the state of the cell and the continual communication of information among neighboring cells and between different tissues. In particular, elaborate mechanisms maintain coordination of the various stages of the cell cycle and permit cell cycle progression only under the proper environmental circumstances. Other elaborate mechanisms essentially continually assess the status of surviving cells, and, if abnormal cells are detected, these mechanisms induce a program of self-destruction called apoptosis. Cancer is a genetic disease of somatic cells. In cancer cells, multiple mutations arise that disrupt both of these processesin some cases, the cancer-promoting mutations directly affect these processes, whereas, in other cases, cancer-promoting mutations elevate the overall mutation rate of the cell. Both gain-of-function oncogene mutations and loss-of-function tumor-suppressor gene mutations can contribute to the tumor progression process through the uncoupling of the normal controls that hold the cell cycle in check or promote apoptosis.

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