Ovarian Cancer Coverage from Every Angle

Incomplete Pregnancy and Risk of Invasive Ovarian Cancer

By: Sarah Campen, PharmD
Posted: Monday, September 14, 2020

The relationship between parity and a decreased risk of invasive ovarian cancer is well established; now, the results of a pooled analysis published in the Journal of the National Cancer Institute indicate that incomplete pregnancy appears to be associated with a reduced risk of ovarian cancer as well. This inverse association was “broadly consistent” across histotypes but was most apparent for clear cell ovarian cancer.

“Future research should focus on understanding the mechanisms underlying the reduced risk associated with complete and incomplete pregnancies to shed light on ovarian cancer etiology,” stated Celeste Leigh Pearce, PhD, of the University of Michigan School of Public Health, Ann Arbor, and colleagues.

The analysis included 10,470 patients with invasive epithelial ovarian cancer and 16,942 controls from 15 case-control studies from the Ovarian Cancer Association Consortium. Ever having an incomplete pregnancy was associated with a 16% reduction in ovarian cancer risk (P < .001), and there was a trend of decreasing risk with an increasing number of incomplete pregnancies (P < .001). This inverse association was observed in 11 of the 15 studies—with results from 4 studies reaching statistical significance—whereas the results for the remaining 4 studies were null.

Of note, the inverse association for an incomplete pregnancy was weaker than that of a complete pregnancy, but the authors noted that the odds ratio (OR) for an incomplete pregnancy (0.86) was approximately what would be expected based on an OR for a complete pregnancy (0.75), given the difference in duration. Although the inverse association with incomplete pregnancy was seen for each histotype, the magnitude of the association for patients with two or more incomplete pregnancies was weakest for high-grade serous disease (OR = 0.93) and strongest for clear cell disease (OR = 0.39).

Disclosure: The study authors reported no conflicts of interest.

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