[What is a targeted therapy? The view of the biologist]

Cancer chemotherapy, which followed a continuous progression all along the second half of the 20th century, is now undergoing profound changes: instead of focusing exclusively on the inhibition of cell proliferation, new developments now focus the mechanisms of oncogenesis. The name of "targeted therapy" refers to the targeting of oncogenesis. Understanding the mechanisms of oncogenesis is a requirement for the understanding of the use of targeted therapies. Each tumour follows its own natural history and characteristic oncogenic alterations, which define the potential targets for novel molecules. Prescribing targeted chemotherapy cannot be carried out without prior characterisation of the tumour, with the identification, among the various oncogenic alterations present, of the alteration to be targeted. As a consequence, it is mandatory to conceive this novel chemotherapy only on the basis of the selection of the patients who would benefit of it. This didactic review presents the general aspects of the molecular alterations of cancers, the potential targets which ensue, and the ways presently available to reach them.