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Family history of breast/ovarian cancer and referral criteria for a BRCA1 testing program Bajdik, Christopher Douglas

Abstract

Background: Breast and ovarian cancer can arise from genetic predisposition and environmental (i.e., non-genetic) exposures. Family history is the basis for many referrals to a genetic testing program, but family history is expected to depend on a person's age and family structure, the disease risk that is associated with BRCA1 and the sporadic disease risk in the population. Population-based research on BRCA1 is difficult to conduct because of logistic, financial and ethical issues. Methods: The first phase of the study created a simulation model of BRCA1 and breast/ovarian cancer in a family. The next phase analyzed the effects of age and pedigree size on the relationship between family history and whether someone carried a BRCA1 mutation, and examined the stability of results in relation to estimates of the hereditary and overall rate of breast/ovarian cancer in the population. The third phase combined the simulation results with BC demographic information to examine the implications for a provincial genetic testing program. Results: The predictive accuracy of family history was strongly dependent on a person's age and pedigree size. The stability of these results also depended on the risk associated with a BRCA1 mutation and the population rate of disease in the model. If 0.12% of people in BC carry a mutation, a province-wide testing program for persons 20 to 69 years of age is estimated to identify 62% of them. About 4% of people who receive testing will be BRCA1 mutation carriers. Both percentages depend on referral criteria for the program. Conclusions: The results of these analyses are based on assumptions and observations in other populations. The corresponding information for the British Columbia population is not known. Any criteria that restrict referral to a BRCA1 testing program will exclude some mutation carriers in the population. The part of the population most likely to be affected is young people with small families.

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