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Parity is associated with better prognosis in ovarian germ cell tumors, but not in other ovarian cancer subtypes

Ovarian cancer is influenced by reproductive factors, with a reduced risk of epithelial ovarian cancer in parous women. Nonepithelial ovarian cancer frequently affects young women and often precedes or occurs during the childbearing years. However, the impact of reproductive factors on ovarian cancer survival remains unclear: in epithelial ovarian cancer, data are conflicting, and subtype‐specific associations have not been examined, and in nonepithelial ovarian cancer, it has not been studied. Using Swedish registers, we evaluated associations between women's reproductive history and cancer‐specific mortality by subtype of epithelial and nonepithelial ovarian cancer in 3791 women born 1953 and later, diagnosed from 1990 to 2018. Hazard ratios (HRs) with 95% confidence intervals (95% CIs) were calculated using Cox‐proportional hazard models. Parity was associated with a 78% decreased risk of cause‐specific mortality in 243 women with germ cell tumors (GCTs) (parous vs nulliparous, adjusted for age at diagnosis: HR: 0.22 [95% CI 0.07‐0.62]), with a decreased risk with increasing number of births (per birth: HR: 0.60 [95% CI 0.38‐0.95]). We found no evidence of associations between parity and cause‐specific mortality among the 334 patients with sex‐cord stromal tumors, nor among the 3214 patients with epithelial ovarian cancer; neither overall, nor by subtype. In conclusion, in our large, population‐based study, parity was associated with a clearly better prognosis in GCTs but not in the other ovarian cancer subtypes. Future research on how hormone exposure impacts GCT development may lead to a better understanding of mechanisms affecting survival.