Stratifying the risk of ovarian cancer incidence by histologic subtypes in the Korean Epithelial Ovarian Cancer Study (Ko‐EVE)

Abstract Introduction This study aimed to verify the association between ovarian cancer (OC) and reproductive‐ and lifestyle‐related risk factors stratified by the subtype of OC. Methods In this matched case–control study derived from the Korean epithelial ovarian cancer study (Ko‐EVE), we calculated the risk of OC subtypes using odds ratios (ORs) and 95% confidence intervals (95% CIs) in a logistic regression model. Results As a result of matching, 531 cases and 2,124 controls were selected. Smoking had positive association with high‐grade serous (HGS) OC (OR = 2.69, 95% CI = 1.15–6.30), whereas alcohol consumption had positive association with mucinous type (MUC) (OR = 3.63, 95% CI = 1.39–9.49). Obesity (≥30 kg/m2) was associated with clear cell type (CLC) (OR = 4.57, 95% CI = 1.06–19.77). Spontaneous abortion was negatively associated with CLC (OR = 0.34, 95% CI = 0.13–0.90), in contrast to HGS (OR = 1.43, 95% CI = 0.96–2.15). Tubal ligation, hysterectomy, and oophorectomy were associated with decreased risk of HGS (OR = 0.14, 95% CI = 0.05–0.39; OR = 0.23, 95% CI = 0.07–0.73; OR = 0.28, 95% CI = 0.08–0.97, respectively). Early menarche was strongly associated with increased risk of CLC, but not MUC (OR = 6.11, 95% CI = 1.53–24.42; OR = 3.23, 95% CI = 0.98–10.86). Further, childbirth (≥2 times) was negatively associated with endometrioid type OC and CLC (OR = 0.11, 95% CI = 0.04–0.35; OR = 0.12, 95% CI = 0.02–0.37, respectively). Oral contraceptives and hormone replacement therapy were negatively associated with OC (OR = 0.61, 95% CI = 0.40–0.93; OR = 0.51, 95% CI = 0.32–0.80, respectively), and similar negative associations were also observed in HGS (OR = 0.69; OR = 0.60, respectively). Associations between family history of breast cancer and OC, regular exercise (≥5/week), and artificial abortion and OC were similar across all subtypes (OR = 3.92; OR = 0.41; OR = 0.72, respectively). Conclusion A heterogeneous association between some risk factors and the incidence of each subtype of epithelial OC was observed, suggesting that the carcinogenic mechanisms of each subtype may be partly different.