Familial predisposition to breast cancer in a British population: implications for prevention

The aims of this study were to estimate the familial relative risk of breas t cancer according to the age of the at risk individual and the age at whic h the relative was affected, and to estimate the proportion of the general population in several breast cancer risk categories because of a family his tory and. thus estimate the potential to reduce the overall breast cancer b urden using interventions targeted at women at increased risk because of fa mily history. Familial relative risks were computed by comparing breast can cer incidence in relatives of 2809 breast cancer cases From a population ba sed case series with that expected from general population incidence rates. The proportion of the general population in different categories of risk a ccording to family history was estimated from the relative risk of breast c ancer for that category and the proportion of cases in that category. 389 ( 13.8%) cases had at least 1 first degree relative with boast cancer, The re lative risk of breast cancer in sisters of index cases was 1.90 (95% confid ence interval (CI) 1.53-2.36) and that in mothers 1.73 (1.52-1.97). The ris k to mothers of cases diagnosed under 50 years of age tended to decrease in older mothers, but no age effect was seen for mothers of cases diagnosed g reater than or equal to 50 years of age. There was no evidence that relativ e risk to sisters declined with age. For women with 2 affected first degree relatives the relative risk was 2.85 (2.12-3.76). From these data, we esti mate that in the general population 6.8% of women under the age of 50 years and 9.7% of women aged 50-65 years have at least 1 first degree relative a ffected with breast cancer. Two per cent of women under 50 years have a fam ily history which confers an increased risk of at least 2.5-fold. An interv ention targeted at this group that reduced breast cancer morbidity by 20% w ould reduce the total burden of breast cancer in this age group by 1.1% at most. A family history of breast cancer is quite common in the general popu lation, but preventive interventions targeted at women at high risk of brea st cancer because of Family history will have limited impact on breast canc er morbidity as a whole. (C) 2000 Published by Elsevier Science Ltd. All ri ghts reserved.