Expanding Our Understanding of Ovarian Cancer Risk: The Role of Incomplete Pregnancies.
- Department of Public Health, California State University, Fullerton, Fullerton, CA, USA.
- Department of Epidemiology, University of Michigan School of Public Health, Ann Arbor, MI, USA.
- School of Women's and Children's Health, Faculty of Medicine, University of NSW Sydney, Sydney, New South Wales, Australia.
- Adult Cancer Program, Lowy Cancer Research Centre, University of NSW Sydney, Sydney, New South Wales, Australia.
- MRC Clinical Trials Unit, Institute of Clinical Trials & Methodology, University College London, London, UK.
- Department of Epidemiology, Genetic Epidemiology Research Institute, University of California Irvine, Irvine, CA, USA.
- Department of Biomedical Data Science, Stanford University School of Medicine, Stanford, CA, USA.
- Division of Cancer Epidemiology and Genetics, National Cancer Institute, Bethesda, MD, USA.
- Cancer Prevention and Control Program, Rutgers Cancer Institute of New Jersey, New Brunswick, NJ, USA.
- Department of Epidemiology, Harvard TH Chan School of Public Health, Boston, MA, USA.
- Departments of Epidemiology and of Pediatrics, Geisel School of Medicine at Dartmouth, Hanover, NH, USA.
- Department of Public Health Sciences, University of Virginia, Charlottesville, VA, USA.
- Department of Obstetrics and Gynecology, Duke University Medical Center, Durham, NC, USA.
- Division of Epidemiology, Department of Health Science Research, Mayo Clinic, Rochester, MN, USA.
- Department of Virus, Lifestyle and Genes, Danish Cancer Society Research Center, Copenhagen, Denmark.
- Population Health Department, QIMR Berghofer Medical Research Institute, Brisbane, Queensland, Australia.
- School of Public Health, University of Texas Health Science Center at Houston, Houston, TX, USA.
- Womens Cancer Research Center, Magee-Womens Research Institute and Hillman Cancer Center, Pittsburgh, PA, USA.
- Division of Cancer Prevention and Control, Roswell Park Comprehensive Cancer Center, Buffalo, NY, USA.
- Samuel Oschin Comprehensive Cancer Institute, Cancer Prevention and Genetics Program, Cedars-Sinai Medical Center, Los Angeles, CA, USA.
- Department of Obstetrics and Gynecology, John A. Burns School of Medicine, University of Hawaii, Honolulu, HI, USA.
- Division of Cancer Epidemiology, German Cancer Research Center, Heidelberg, Germany.
- Program in Epidemiology, Division of Public Health Sciences, Fred Hutchinson Cancer Research Center, Seattle, WA, USA.
- Department of Population Health Sciences, Huntsman Cancer Institute, University of Utah, Salt Lake City, UT, USA.
- Chronic Disease Epidemiology, Yale School of Public Health, New Haven, CT, USA.
- Department of Biostatistics, University of Michigan School of Public Health, Ann Arbor, MI, USA.
- Department of Oncology, University of Cambridge, Cambridge, UK.
- Department of Preventive Medicine, Keck School of Medicine, University of Southern California Norris Comprehensive Cancer Center, Los Angeles, CA, USA.
BACKGROUND: Parity is associated with decreased risk of invasive ovarian cancer; however, the relationship between incomplete pregnancies and invasive ovarian cancer risk is unclear. This relationship was examined using 15 case-control studies from the Ovarian Cancer Association Consortium (OCAC). Histotype-specific associations, which have not been examined previously with large sample sizes, were also evaluated.
METHODS: A pooled analysis of 10 470 invasive epithelial ovarian cancer cases and 16 942 controls was conducted. Odds ratios (ORs) and 95% confidence intervals (CIs) for the association between incomplete pregnancies and invasive epithelial ovarian cancer were estimated using logistic regression. All models were conditioned on OCAC study, race and ethnicity, age, and education level and adjusted for number of complete pregnancies, oral contraceptive use, and history of breastfeeding. The same approach was used for histotype-specific analyses.
RESULTS: Ever having an incomplete pregnancy was associated with a 16% reduction in ovarian cancer risk (OR = 0.84, 95% CI = 0.79 to 0.89). There was a trend of decreasing risk with increasing number of incomplete pregnancies (2-sided Ptrend < .001). An inverse association was observed for all major histotypes; it was strongest for clear cell ovarian cancer.
CONCLUSIONS: Incomplete pregnancies are associated with a reduced risk of invasive epithelial ovarian cancer. Pregnancy, including incomplete pregnancy, was associated with a greater reduction in risk of clear cell ovarian cancer, but the result was broadly consistent across histotypes. Future work should focus on understanding the mechanisms underlying this reduced risk.