[Breast cancer in women with trisomy 21].

The population with Down's syndrome has a different cancer profile compared to the general population, even after taking into account issues of survival and ageing. Several solid tumours are unusually rare, whereas in contrast leukaemias are increased. In addition, few studies are available on this topic. We therefore decided to conduct a mortality study based on the INSERM national mortality statistics in France comparing over a 24 year period deaths from female breast cancer in the general French population with the cancer deaths in women with Down's syndrome. Only 5 deaths with Down's syndrome could be found compared to 68.98 expected based on national statistics. This clear reduction in risk agrees with other studies available in Down's syndrome patients. This observation could be partly explained by over expression of genes linked to gene dosage effects on chromosome 21, playing a role in cell growth, differentiation, survival and death. An additional protective effect could come from the marked and continued decreased exposure to oestrogens, starting in utero for women with trisomy 21 and lasting all over life.