Supplementary Table 1. Clinical characteristics of BRCA1/2 carriers including index cases in the Northern Netherlands (study population) and in the rest of the Netherlands (reference population). Supplementary Table 2. Overview of number of carriers (excluding index cases) at risk at each age-decade and number of breast cancer event for each age-decade. Supplementary Table 3. Cumulative incidence of breast cancer in BRCA1/2 carriers, excluding index cases, in the study population (Northern Netherlands) and reference population (rest of the Netherlands). Estimation of risks weighted to an equal contribution from the different birth cohorts in each population. Supplementary Table 4. Relative risks (hazard ratios (95% confidence interval)) of breast cancer for mutation spectrum, excluding index cases. Supplementary Table 5. Regional differences in the breast cancer risk of BRCA1/2 carriers including index cases (adjusted for birth year) in the Netherlands: the study population (Northern Netherlands) compared to the reference population (the rest of the Netherlands.)
ARTICLE ABSTRACT
Background: We aimed to quantify previously observed relatively high cancer risks in BRCA2 mutation carriers (BRCA2 carriers) older than 60 in the Northern Netherlands, and to analyze whether these could be explained by mutation spectrum or population background risk.Methods: This consecutive cohort study included all known pathogenic BRCA1/2 carriers in the Northern Netherlands (N = 1,050). Carrier and general reference populations were: BRCA1/2 carriers in the rest of the Netherlands (N = 2,013) and the general population in both regions. Regional differences were assessed with HRs and ORs. HRs were adjusted for birth year and mutation spectrum.Results: All BRCA1 carriers and BRCA2 carriers younger than 60 had a significantly lower breast cancer risk in the Northern Netherlands; HRs were 0.66 and 0.64, respectively. Above age 60, the breast cancer risk in BRCA2 carriers in the Northern Netherlands was higher than in the rest of the Netherlands [HR, 3.99; 95% confidence interval (CI), 1.11–14.35]. Adjustment for mutational spectrum changed the HRs for BRCA1, BRCA2 <60, and BRCA2 ≥60 years by −3%, +32%, and +11% to 0.75, 0.50, and 2.61, respectively. There was no difference in background breast cancer incidence between the two regions (OR, 1.03; 95% CI, 0.97–1.09).Conclusions: Differences in mutation spectrum only partly explain the regional differences in breast cancer risk in BRCA2 carriers, and for an even smaller part in BRCA1 carriers.Impact: The increased risk in BRCA2 carriers older than 60 may warrant extension of intensive breast screening beyond age 60. Cancer Epidemiol Biomarkers Prev; 23(11); 2482–91. ©2014 AACR.
