[Genetics and cancers].

Multiple genome alterations can be seen within a tumor and continue to accumulate throughout development of the growth. Chromosome deletions occurring in tumors are generating much interest. To date, the best known model is retinoblastoma whose study gave rise to the concepts of anti-oncogene or tumor suppressor gene. Studies of genetic anomalies in colorectal tumors have led to an elegant model of colonic carcinogenesis in which multiple steps, each with its corresponding genetic anomaly, successively accumulate, with deletion of the p53 gene occurring as a late event. Successive anomalies of the p53 gene (mutations, deletions) occur during passage from a low-grade astrocytoma to a higher-grade astrocytoma. Studies of familial forms of breast cancer and of breast and ovarian cancer have also provided insight into the biology of these tumors, with the identification of a predisposing chromosomal area whose location is 17 q-12-21. These approaches open up possibilities for screening techniques and use of preventive treatments in highly selected patients. However they raise many ethical problems. There is a need for developing a charter for these family studies in the near future.