Incomplete pregnancies linked to reduced risk for ovarian cancer
Incomplete pregnancies appeared associated with reduced risk for invasive epithelial ovarian cancer, according to results of a study published in Journal of the National Cancer Institute.
Researchers observed an association between all pregnancy, including incomplete pregnancies, and a greater reduction in risk for clear cell ovarian cancer, with broad consistency across histotypes.
“Considering the evidence from all of the studies on incomplete pregnancies, having an incomplete pregnancy appears to be associated with decreased risk [for] ovarian cancer,” Alice W. Lee, PhD, assistant professor in the department of public health at California State University, and colleagues wrote. “Interestingly, this inverse association with incomplete pregnancies has also been observed in endometrial cancer, which shares similar risk factors with ovarian cancer.”
Parity has been associated with lower risk for invasive ovarian cancer; however, the relationship between incomplete pregnancies and risk for invasive ovarian cancer remained unclear, according to study background.
To study this association, Lee and colleagues retrospectively analyzed 10,470 women with invasive epithelial ovarian cancer and 16,942 controls from 15 case-control studies from the Ovarian Cancer Association Consortium.
Researchers used logistic regression to estimate ORs and conditioned all models by race/ethnicity, age and education level. They adjusted for number of complete pregnancies, use of oral contraceptives and history of breastfeeding. They used the same approach for histotype-specific analyses.
Among all cases, 32.3% reported ever experiencing an incomplete pregnancy compared with 38% of the controls.
Results showed an association between ever having an incomplete pregnancy and a 16% reduction in risk for ovarian cancer (OR = 0.84; 95% CI, 0.79-0.89).
Specifically, women who reported one incomplete pregnancy had a 14% decreased risk (OR = 0.86; 95% CI, 0.81-0.92), whereas those who reported two or more incomplete pregnancies had a 20% decreased risk (OR = 0.8; 95% CI, 0.74-0.87).
Women who had completed pregnancies demonstrated greater reductions in risk, including 25% with one pregnancy (OR = 0.75; 95% CI, 0.68-0.83), 41% with two pregnancies (OR = 0.59; 95% CI, 0.54-0.65) and 49% with three pregnancies (OR = 0.51; 95% CI, 0.47-0.57).
The investigators identified inverse associations in 11 of the 15 studies, as well as for all major ovarian cancer histotypes, from the weakest for high-grade serous (OR = 0.93; 95% CI, 0.84-1.03) to the strongest for clear cell (OR = 0.39; 95% CI, 0.28-0.53).
“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,” Lee and colleagues wrote.