[Biology of solid cancers: breast cancer as an example. First part: genetic systems implicated in carcinogenesis]

There are two main categories of genes involved in cancer: protoconcogenes and tumor suppressor genes. The development of cancer can require the production of several successive gene accidents within a given cell. Most of these alterations appear to be somatic changes. Only one of these two steps would involve germinal processes and only in hereditary tumors. When altered, these genes, implicated in cell proliferation, differentiation and normal cell death, contribute to the initiation and/or the progression of tumors. Other genes have an indirect effect on the malignant transformation and thus complete the action of oncogenes and suppressor genes at certain stages of cancerogenesis. The genes implicated in individual susceptibility to cancer is an example (genes coding for DNA repair enzymes and for proteins which inactivate exogenous cancerogenenic agents. Others are genes coding for growth factors and angiogenic factors, genes involved in metastatic dissemination including those which code for proteases and adherence proteins, and finally genes affecting chemoresistance.