Five to ten percent of all breast cancers arise from germ-line mutations in high-penetrance breast cancer susceptibility genes such as BRCA1, BRCA2, p53 and PTEN, and confer a high individual risk for developing hereditary breast cancer.1 The BRCA1 gene is located on the long arm of chromosome 17, while BRCA2 is located on the long arm of chromosome 13. Gene-positive patients have an 80% risk of developing breast cancer especially in the pre-menopausal age group.2
Aguas et al. observed that BRCA1 and BRCA2 predispose a woman to breast cancer in only 5–10% of the total number of breast cancers and believe that even though family history may reflect shared genes, it may also suggest shared environmental lifestyle exposures.8 They therefore advised that due to ethical and legal issues, as well as psychological consequences, genetic screening should only be carried out in the research settings, rather than in routine clinical practice.8 But we know that genetic screening is carried out selectively in affected families.
Furthermore, Russell et al. agreed on the presence of polymorphisms in breast cancer susceptibility genes with low penetrance, which have a greater contribution to breast cancer pathogenesis in combination with exogenous factors such as diet, alcohol and pollution, as well as endogenous factors such as oestrogens and progesterone exposures.2 This accounts for majority of the sporadic (non-familial) breast cancers which form 90–95% of all breast cancers in women. The familial cancers usually occur in younger patients, are often multi-focal or bilateral and have poorer prognosis, compared with the sporadic cases, which are mostly unilateral, occurring in older patients and have better outcomes