Expanding Our Understanding of Ovarian Cancer Risk: The Role of Incomplete Pregnancies

Alice W. Lee, Stacey Rosenzweig, Ashley Wiensch, Susan J. Ramus, Usha Menon, Aleksandra Gentry-Maharaj, Argyrios Ziogas, Hoda Anton-Culver, Alice S. Whittemore, Weiva Sieh, Joseph H. Rothstein, Valerie Mcguire, Nicolas Wentzensen, Elisa V. Bandera, Bo Qin, Kathryn L. Terry, Daniel W. Cramer, Linda Titus, Joellen M. Schildkraut, Andrew BerchuckEllen L. Goode, Susanne K. Kjaer, Allan Jensen, Susan J. Jordan, Roberta B. Ness, Francesmary Modugno, Kirsten Moysich, Pamela J. Thompson, Marc T. Goodman, Michael E. Carney, Jenny Chang-Claude, Mary Anne Rossing, Holly R. Harris, Jennifer Anne Doherty, Harvey A. Risch, Lilah Khoja, Aliya Alimujiang, Minh Tung Phung, Katharine Brieger, Bhramar Mukherjee, Paul D.P. Pharoah, Anna H. Wu, Malcolm C. Pike, Penelope M. Webb, Celeste Leigh Pearce

Research output: Contribution to journalArticlepeer-review


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.

Original languageEnglish (US)
Pages (from-to)301-308
Number of pages8
JournalJournal of the National Cancer Institute
Issue number3
StatePublished - Mar 1 2021

ASJC Scopus subject areas

  • Oncology
  • Cancer Research


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