Screening women at high risk for breast cancer: one program fits all? : Subgroup analysis of a large population high risk breast screening program.

INTRODUCTION: The Ontario High Risk Breast Screening program follows women aged 30-69 at an increased risk of breast cancer, using a yearly mammography and breast MRI. The aim of this study is to determine the clinical outcomes for the enrolled women. METHODS: Observational cohort study following 2081 participants in the high-risk screening program 2011-2017. The participants were divided into three subgroup according to their risk criteria: (a) known carriers of pathogenic variants (PV) in hereditary breast cancer genes. (b) Previous chest radiotherapy. (c) Estimated life time risk (ELR) ≥ 25%, calculated using the International Breast Cancer Intervention Study (IBIS) tool, with no known mutation or previous radiation. All Breast Cancer (BC) diagnosed during the follow-up time were recorded. RESULTS: 673 women carried PVs in hereditary breast cancer genes, 159 had a history of chest radiotherapy, and 1249 had an ELR ≥ 25%. The total cohort of screening years was 8126. Median age at BC diagnosis was 41 for the first group, 47 for the second group and 51 for the third. BC incidence rate was 18.2 for PV mutation carriers, 17.9 for the chest radiotherapy group and 6.2 for ELR ≥ 25%. Hazard ratio was similar for the first two groups, but significantly lower for the ELR ≥ 25% group. When stratifying by age, the incidence rate in the ELR ≥ 25% increased over time, until it became similar to that of the other subgroups after age 50. CONCLUSION: Our findings question the need to screen women with an elevated lifetime risk using the same screening practices used for women who are PV mutation carriers, or with a history of chest radiation, prior to the age of 50.