Breast cancer risk estimations are both informative and useful at the population level, with many screening programs relying on these assessments to allocate resources such as breast MRI. This crosssectional multicenter study attempts to quantify the breast cancer risk distribution for women between the ages of 40 to 79 years undergoing screening mammography in British Columbia (BC), Canada. The proportion of women at high breast cancer risk was estimated by surveying women enrolled in the Screening Mammography Program of British Columbia (SMPBC) for known breast cancer risk factors. Each respondent's 10-year risk was computed with both the Tyrer-Cuzick and Gail risk assessment models. The resulting risk distributions were evaluated using the guidelines from the National Institute for Health and Care Excellence (United Kingdom). Of the 4,266 women surveyed, 3.5% of women between the ages of 40 to 79 years were found to have a high 10-year risk of developing breast cancer using the Tyrer-Cuzick model (1.1% using the Gail model). When extrapolated to the screening population, it was estimated that 19,414 women in the SMPBC are considered to be at high breast cancer risk. These women may benefit from additional MRI screening; preliminary analysis suggests that 4 to 5 additional MRI machines would be required to screen these high-risk women. However, the use of different models and guidelines will modify the number of women qualifying for additional screening interventions, thus impacting the MRI resources required. The results of this project can now be used to inform decision-making groups about resource allocation for breast cancer screening in BC. Cancer Prev Res; 6(10); 1084-92. Ó2013 AACR.

51 Background: Screening women at high risk with MRI has been shown to detect breast cancer at an early stage. Therefore, MRI screening has been recommended in the UK and USA for women who are at a high risk of developing breast cancer. However, there is no information available in the province of British Columbia (BC) about the number of women who have a high risk of developing breast cancer. Therefore, we carried out a study to estimate the breast cancer risk distribution in three sample populations in BC using Tyrer-Cuzick (TC) risk prediction model so that additional resource requirement for MRI breast screening can be calculated. Methods: A survey questionnaire was designed based on the TC model, which includes family history, hormonal factors, and benign breast disease. Additional questions also include factors that are used in other models (Gail, Claus, and BCRAPRO) as well as factors that may be included in the future. Women were recruited by staff and volunteers at three screening mammography clinics: Kelowna, Victoria General Hospital, and BC Women’s Health Centre in Vancouver. The survey was available to women to complete on the web, by phone, or on paper. An online database was constructed to store and query the data. The 10-year risk of developing breast cancer for each woman was calculated using the Tyrer-Cuzick IBIS Risk Evaluator software and the risk distribution of the survey population was analyzed. Results: Data from 3,200 women recruited from three sites, gives a risk distribution showing 2.6% are at high risk of developing breast cancer, 31.2% are at moderate risk, and 66.2% are at low risk. Based on NICE guidelines (UK), high risk is defined as having a 10-year risk of greater than 8%, moderate risk as 3-8%, and low risk as less than 3%. Extrapolating this to the approximately 500,000 women who are eligible to attend for screening mammography in BC, 13,000 women are considered at high risk. Conclusions: Our results indicate that 2.6% of women ages 40-79 attending screening mammography in BC may have a very high risk of developing breast cancer based on personal and family history. Based on a 14-hour work day, three additional MRI scanners would be required to implement MRI screening for these high-risk women in BC.