Early pregnancy IGF‐I and placental GH and risk of epithelial ovarian cancer: A nested case‐control study

Insulin‐like growth factor‐I (IGF‐I) signaling may promote ovarian tumor development by exerting mitotic, antiapoptotic and proangiogenic effects. During pregnancy, maternal production of IGF‐I is regulated by placental growth hormone (GH). Parity is an established protective factor for ovarian cancer, however, no prior study has evaluated placental GH and IGF‐I in pregnancy and epithelial ovarian cancer (EOC). Prior prospective studies on the association between IGF‐I and EOC in nonpregnant populations were inconclusive and did not address associations in subtypes of EOC. Among members of the Finnish Maternity Cohort and the Northern Sweden Maternity Cohort, we identified 1,045 EOC cases, diagnosed after recruitment (1975–2008) and before March 2011 and 2,658 individually matched controls. Placental GH and IGF‐I were measured in serum from the last pregnancy before EOC diagnosis or selection as control. We used conditional logistic regression to estimate odds ratios (ORs) and 95% confidence intervals (CIs) for tertiles and a doubling of hormone concentrations. Higher IGF‐I was associated with a nonsignificant decrease in risk for invasive OR_{T3 vs. T1}: 0.79 (0.62–1.02); p_trend = 0.07] and endometrioid tumors OR_{T3 vs. T1}: 0.55 (0.28–1.07); p_trend = 0.07]. The protective association between higher IGF‐I levels and risk of invasive EOC was stronger in analyses limited to women aged <55 years at diagnosis OR_{T3 vs. T1}: 0.74 (0.57–0.96); p_trend = 0.03]. Our study provides the first data on placental GH and IGF‐I in pregnancy and EOC risk overall and by subtype. Our data suggest higher IGF‐I levels in pregnancy may be associated with lower risk of invasive and endometrioid EOC.