[Genetic predispositions to breast cancer].

Genetic epidemiology and position cloning techniques have made it possible to estimate the risk women with a family history of breast cancer have of developing a breast tumor. THREE PREDISPOSITION GENES: Three BReast CAncer genes (BRCA1, BRCA2 and BRCA3) have been localized on chromosomes 17 13 and 8. It is highly likely that other genes also have an influence. GENETIC TESTING: When an altered BRCA1 or BRCA2 gene is identified in a family, a gene test can be proposed to recognize predisposition in relatives. A negative test means the subject is not predisposed to breast cancer and that transmission to offspring is not possible. Inversely, the risk of breast cancer is high if the mutation is detected, raising the difficult problem of counselling, particularly in young subjects. PROBLEMS RELATED TO SCREENING TESTS: Screening tests can only be undertaken if the "candidate" is aware of the consequences of the screening results and has had enough time to make a fully informed decision. Confidentiality must be particularly strict, particularly in the field of employment and insurance.