Multiple births and risk of epithelial ovarian cancer

Background and Methods: Prevailing hypotheses about the causes of ovarian c arcinogenesis predict that women with a history of multiple births (twins, triplets, etc.) should be at increased risk of epithelial ovarian cancer. H owever, the scant available evidence suggests that they may actually be at lower risk. To resolve this issue, we pooled data from eight studies involv ing 2859 parous women with epithelial ovarian cancer (case patients) and 74 34 parous women without ovarian cancer (control women). In addition to asse ssing their history of multiple births (and the sex of the children, where available), we obtained information on age, parity, oral contraceptive use, and other reproductive factors for each woman. Details of tl:mor histology were available for all case patients. We estimated the relative risks of v arious histologic types of ovarian cancers associated with multiple births by using multivariable logistic regression analysis, adjusting for matching and confounding variables. Results: Among these parous women, 73 case pati ents (2.6%) and 257 control women (3.5%) had a history of multiple births. The adjusted summary odds ratio (OR) for developing all types of epithelial ovarian cancer that are associated with multiple births was 0.81 (95% conf idence interval [CI] = 0.61-1.08), We found no evidence that risks associat ed with multiple births differed among women with borderline or invasive tu mors and among women with same-sex and opposite-sex offspring from multiple births. The risk reductions appeared specific for nonmucinous tumors (n = 2453; summary adjusted OR = 0.71 [95% CI = 0.52-0.98]); in contrast, associ ations with mucinous tumors (n = 406) were heterogeneous across studies. Co nclusions: Parous women with nonmucinous ovarian cancer are no more likely to have a history of multiple births than other parous women, counter to th e predictions of current hypotheses for causes of ovarian cancer.