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Breast cancer is common in the general population, affecting one woman in every 12. About 5% of breast cancers are caused by dominantly inherited high risk susceptibility mutations in genes such as BRCA1 and BRCA2.1–4 Another, larger proportion may be caused by mutations in (as yet) unidentified lower penetrance genes, because even where such high risk mutations are not implicated, a family history of breast cancer increases a woman's lifetime risk of developing the disease herself.2 There are no external markers of risk (no phenotype) to help identify those who carry a faulty gene, except in very rare cases such as Cowden's disease.5 In order to assess the likelihood of there being a predisposing mutation in a family, it is necessary to assess the family tree. Inheritance of a germline mutation can cause the disease at a young age and often, if the woman survives, cancer in the contralateral breast. Some gene mutations may give rise to susceptibility to other cancers, such as ovary, colon, and sarcomas.6–9 Multiple primary cancers in one woman or early onset cancers in the women or their relatives are, therefore, suggestive of a predisposing gene.
Apart from family history, age, gender, and previous cancer, other risk factors include exposure to oestrogen,10 alcohol, weight gain, and the presence of proliferative breast disease.11,12 The management options for a woman with a significantly increased risk are limited. She may choose to do nothing. To reduce her risk, a woman can plan to limit prolonged use of the oral contraceptive pill (OCP) and hormonal replacement therapy (HRT) and prevent weight gain. Clinical management options include screening by mammography, prophylactic mastectomy, artificial early menopause (oophorectomy), and anti-oestrogen therapy (the subject of a current clinical trial (RAZOR)). Assessment of risk factors, …