Effects of risk factors for ovarian cancer in women with and without endometriosis.

Objective: To evaluate the associations between 10 well-established ovarian cancer risk factors and risk of ovarian cancer among women with vs. without endometriosis.

Design: Pooled analysis of 9 case-control studies in the Ovarian Cancer Association Consortium.

Setting: Population-based.

Patient(s): We included 8,500 women with ovarian cancer, 13,592 control women.

Intervention(s): Ten well-established ovarian cancer risk factors.

Main Outcome Measure(s): Risk of ovarian cancer for women with and without endometriosis.

Result(s): Most risk factor-ovarian cancer associations were similar when comparing women with and without endometriosis, and no interactions were statistically significant. However, body mass index (BMI) 25-<30 kg/m was associated with increased ovarian cancer risk among women with endometriosis (odds ratio [OR] = 1.27, 95% confidence interval [CI] 1.00-1.60), but not associated with the risk among women without endometriosis (OR = 0.97; 95% CI, 0.91-1.05) when compared with BMI 18.5-<25 kg/m; an increased risk was observed for a BMI ≥30 kg/m, although there was little difference comparing women with endometriosis (OR = 1.21; 95% CI, 0.94-1.57) to women without (OR = 1.13; 95% CI, 1.04-1.22) (P-interaction = .51). Genital talcum powder use and long-term menopausal estrogen-only therapy use showed increased ovarian cancer risk, but risk appeared greater for those with endometriosis vs. those without (genital talcum powder: OR = 1.38; 95% CI, 1.04-1.84 vs. OR = 1.12; 95% CI, 1.01-1.25, respectively; ≥10 years of estrogen-only therapy: OR = 1.88; 95% CI, 1.09-3.24 vs. OR = 1.42; 95% CI, 1.14-1.76, respectively); neither of these interactions were statistically significant (P-interaction = .65 and P-interaction = .96, respectively).

Conclusion(s): The associations between ovarian cancer and most risk factors were similar among women with and without endometriosis. However, there was some suggestion of differences by endometriosis status for BMI, menopausal hormone therapy use, and genital talcum powder use, highlighting the complexity of ovarian cancer etiology.