It is estimated that 5-10% of female breast cancer is due to inheritance of a mutated copy of either BRCA1 or BRCA2. Women who inherit a mutated copy of either gene have an elevated lifetime risk of breast cancer—up to 87% by the age of 70 years. There is particular risk of pre-menopausal breast cancer, often before the age of 40 years; there is an associated risk of ovarian cancer (greater with BRCA1); and male carriers are at risk of prostate cancer. Some ethnic groups are at particular risk for carriage of these mutations (estimated 2% of US Ashkenazi Jews).
Other genes contribute less frequently to familial breast cancer. It is hypothesized that ataxia telangiectasia heterozygotes are at risk, but this is as yet unproven. Breast cancer occurs with mutation in PTEN (Cowden disease), MSH1 or MSH2 (HNPCC), and p53 (Li Fraumeni syndrome).
The management of hereditary breast cancer is essentially that of non-hereditary disease. Less clear is how to manage asymptomatic female members of these families. Guidelines suggest referral to medical genetic clinics for counselling, advice on risks, consideration of testing for mutations of BRCA1 and BRCA2, and referral for appropriate further management. Currently, the options open to these women are:
♦ Prophylactic surgery: bilateral subcutaneous mastectomy does reduce the incidence of breast cancer in these women but its impact on survival is uncertain.
♦ Screening: is of unproven benefit in this setting, with uncertainty about the age of first testing, frequency of testing, and the value and risks of frequent mammography.
♦ Breast cancer prevention trials.
Table 17.1 Eligibility criteria for referral to breast cancer families'clinic
♦ Mother or sister developed breast cancer aged <40 years
♦ Mother or sister developed breast cancer aged <50 years and another maternal relative had cancer of the breast, ovary, endometrium, or a sarcoma <65 years
♦ Mother or sister developed breast cancer aged 50-65 years and another maternal relative had cancer of the breast, ovary, endometrium, colorectum, or a sarcoma <50 years
♦ Mother or sister developed double primary cancer (breast plus any of ovary, endometrium, colon, or sarcoma) with at least one tumour before age 50 years and breast cancer before 65 years
♦ Dominant history of breast cancer — 4 or more cases of breast or ovarian cancer on same side of the family at any age
♦ Cancer of colorectum, ovary, endometrium, or sarcoma in mother or father before age 50 years, and at least one first-degree relative with breast cancer age <50 years
♦ Two or more cancers of breast, colorectum, ovary, endometrium, or sarcoma in close relatives of father with at least one before age 50 years
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