A heterogeneous phenotype for age of onset, for cancer development and for cancer spectrum, i.e. different penetrance, has been reported among individuals from families with an identified germline mutation in BRCA1 and BRCA2 genes. Genetic as well as non genetic factors could explain this variation in phenotype. Among genetic causes the type and position of the mutation, allelic variations as well as mutation in other genes could modify breast cancer risk and favour a different phenotype expression. In BRCA1/2 mutation carriers, several studies have been performed in order to evaluate the specific impact on cancer risk of different factors, such as diet, reproduction, anthropometric measures, hormones and environmental exposure. All together these factors can play the role of modifiers of risk in BRCA1/2 mutation carriers.
In this chapter, all those factors have been reviewed as potential modifiers of breast cancer risk in BRCA1 and BRCA2 mutation carriers Moreover, aspects of information and education on modifiers of risk during oncogenetic counseling have been covered.
Keywords: Breast cancer, BRCA genes, cancer risk factors, mutation carriers, ovarian cancer, penetrance, oncogenetic counseling, Menarche, Ovarian Stimulating Drugs, Breastfeeding, Anthropometric Measures
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