Altered growth regulation in cancer

The cell regulation pathways initiated by growth factors may be subverted at several distinct levels in cancer cells. The abnormal production of a growth factor may, through action on its receptor, stimulate aberrant growth. The need for the factor can also be bypassed in several ways. This can occur through the expression of abnormal receptors which no longer require their ligand to generate a signal or through the activation of post receptor processes at key points in the intracellular pathways which normally transduce and modulate the receptor signal. Studies of oncogenes have shown that they may function as abnormal Growth Factors or abnormal receptors, induce expression of potential signal regulators or encode proteins which modulate gene transcription. Such studies offer new clues to mechanisms involved in the causation of cancer.