Signal transduction.

Ordered cell proliferation relies on a complex interplay between diverse cell types, interstitial stroma and organ vasculature. At a cellular level the response to growth stimuli is dependent on the bidirectional exchange of information between the cell membrane and nucleus. Specific regulatory molecules enable the transfer of growth signals and constitute the signal transduction pathways. In malignant disease deregulation of growth regulatory pathways is believed to contribute to the characteristic features of neoplasia, unrestricted cell proliferation, direct invasion of surrounding tissues and the formation of distant metastases. Many proto-oncogenes and oncogenes encode proteins that are strongly suspected to function in aberrant signal transduction (Table 1).