RT Journal Article SR Electronic T1 The Heritability of Breast Cancer among Women in the Nordic Twin Study of Cancer JF Cancer Epidemiology Biomarkers & Prevention JO Cancer Epidemiol Biomarkers Prev FD American Association for Cancer Research SP 145 OP 150 DO 10.1158/1055-9965.EPI-15-0913 VO 25 IS 1 A1 Möller, Sören A1 Mucci, Lorelei A. A1 Harris, Jennifer R. A1 Scheike, Thomas A1 Holst, Klaus A1 Halekoh, Ulrich A1 Adami, Hans-Olov A1 Czene, Kamila A1 Christensen, Kaare A1 Holm, Niels V. A1 Pukkala, Eero A1 Skytthe, Axel A1 Kaprio, Jaakko A1 Hjelmborg, Jacob B. YR 2016 UL http://cebp.aacrjournals.org/content/25/1/145.abstract AB Background: Family history is an established risk factor for breast cancer. Although some important genetic factors have been identified, the extent to which familial risk can be attributed to genetic factors versus common environment remains unclear.Methods: We estimated the familial concordance and heritability of breast cancer among 21,054 monozygotic and 30,939 dizygotic female twin pairs from the Nordic Twin Study of Cancer, the largest twin study of cancer in the world. We accounted for left-censoring, right-censoring, as well as the competing risk of death.Results: From 1943 through 2010, 3,933 twins were diagnosed with breast cancer. The cumulative lifetime incidence of breast cancer taking competing risk of death into account was 8.1% for both zygosities, although the cumulative risk for twins whose co-twins had breast cancer was 28% among monozygotic and 20% among dizygotic twins. The heritability of liability to breast cancer was 31% [95% confidence interval (CI), 10%–51%] and the common environmental component was 16% (95% CI, 10%–32%). For premenopausal breast cancer these estimates were 27% and 12%, respectively, and for postmenopausal breast cancer 22% and 16%, respectively. The relative contributions of genetic and environmental factors were constant between ages 50 and 96. Our results are compatible with the Peto–Mack hypothesis.Conclusion: Our findings indicate that familial factors explain almost half of the variation in liability to develop breast cancer, and results were similar for pre- and postmenopausal breast cancerImpact: We estimate heritability of breast cancer, taking until now ignored sources of bias into account. Cancer Epidemiol Biomarkers Prev; 25(1); 145–50. ©2015 AACR.