Pregnancy complications and subsequent breast cancer risk in the mother: a Nordic population‐based case–control study |
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| Authors: | Rebecca Troisi Anne Gulbech Ording Tom Grotmol Ingrid Glimelius Anders Engeland Mika Gissler Britton Trabert Anders Ekbom Laura Madanat‐Harjuoja Henrik Toft Sørensen Steinar Tretli Tone Bjørge |
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| Affiliation: | 1. Department of Health and Human Services, Division of Cancer Epidemiology and Genetics, National Cancer Institute, National Institutes of Health, Bethesda, MD;2. Department of Clinical Epidemiology, Aarhus University Hospital, Aarhus, Denmark;3. Cancer Registry of Norway, Oslo, Norway;4. Department of Medicine, Clinical Epidemiology Unit, Karolinska Institutet and Karolinska University Hospital, Stockholm, Sweden;5. Department of Immunology, Genetics and Pathology, Uppsala University, Uppsala, Sweden;6. Division of Mental and Physical Health, Norwegian Institute of Public Health, Bergen/Oslo, Oslo, Norway;7. Department of Global Public Health and Primary Care, University of Bergen, Bergen, Norway;8. Information Services Department, National Institute for Health and Welfare (THL), Helsinki, Finland;9. Department of Neurobiology, Care Sciences and Society, Karolinska Institute, Stockholm, Sweden;10. Cancer Society of Finland, Finnish Cancer Registry, Helsinki, Finland;11. Department of Pediatrics, University of Helsinki and Helsinki University Hospital, Helsinki, Finland |
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| Abstract: | Certain features of pregnancy are important risk factors for breast cancer, such as protection afforded by young age at first birth. Preeclampsia, a pregnancy complication, is associated with reduced maternal breast cancer risk. However, questions remain regarding causality, biological mechanisms and the relation of other hypertensive conditions to risk. We conducted a population‐based case–control study of breast cancer cases (n = 116,196) in parous women identified through linkage of birth and cancer registries in Denmark, Finland, Norway and Sweden (1967–2013), including up to 10 matched controls per case (n = 1,147,192) sampled from the birth registries (complete data were not available on all variables). Odds ratios (ORs) with 95% confidence intervals (CIs) were derived from unconditional logistic regression models including matching factors (country, maternal birth year) and parity. Hypertension diagnosed before pregnancy (OR 0.87; 95% CI 0.78–0.97), gestational hypertension (OR 0.90; 95% CI 0.86–0.93) and preeclampsia (OR 0.91; 95% CI 0.88–0.95) were associated with reduced breast cancer risk. Results remained similar after adjustment for smoking and maternal body mass index before first pregnancy, and were generally similar stratified by parity, age at breast cancer diagnosis, time since first and last birth, sex of the offspring and calendar time. Except for retained placenta (OR 1.14; 95% CI 0.98–1.32), no other pregnancy complication appeared associated with breast cancer risk. The mechanisms mediating the modest risk reductions for history of preeclampsia or hypertension preceding or arising during pregnancy, and possible increased risk with history of retained placenta are unknown and warrant further laboratory, clinical and epidemiological investigation. |
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| Keywords: | breast cancer Nordic countries pregnancy preeclampsia hypertension |
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