Targeted drug therapies and cancer.

With the progress of research in molecular biology and greater understanding of cell signalling systems emerge an increasing array of potential targets for the therapy of cancer. While traditional chemotherapy aims to elicit tumour cell death, it also produces undesirable side effects on physiologically proliferating cells. By isolating cell surface receptors which link specific intracellular secondary messenger pathways, researchers are increasingly able to define the biological network which drives cellular function. Of importance are routes involved in malignant transformation, proliferation, survival and angiogenesis. Thus targeted therapy is directed to specific differential growth processes particular to malignant tumours. The principle mode of action generally involves the "lock-and-key" mechanism and identifying the "Achilles' heel" for drug action. Various targeted agents have been studied and many have translated into significant clinical benefit. This chapter will describe some examples which illustrate the role of this approach in gastrointestinal cancers.