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

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/m(2)) 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.