Geontype-phenotype correlations applied for clinical genetics of cancer are finally achieving a dream level.

It is exemplified in a very particular way in chemoprevention, surveillance and chemotherapy directed to BRCA1 mutation carriers. Females with such constitutional abnormalities have initial breast/ovarian cancer risk around 80% during lifetime. According to our latest data it is possible to correlate genotypes, serum selenium level and cancer risk among BRCA1 carriers with very high statistical significance and power. These data strongly suggest that optimization of selenium amount in diet might reduce the risk of breast/ovarian cancer at least three times in around 80% of BRCA1 carriers who should keep serum selenium level around 60-80?g/l and in around 20% carriers with distinct genotype in whom serum selenium level should be above 80 ?g/l. This situation can not be taken as a standard procedure, however even today it is a very attractive option especially that a very low proportion of potential adverse events can be expected due to regulation of selenium level in the body.