Table 2.
Association between hysterectomy for a benign indication and invasive epithelial ovarian cancer, by histologic subtype*
| Adjustment models† | All invasive ovarian cancer HR (95% CI) | Serous HR (95% CI) | Mucinous HR (95% CI) | Endometrioid HR (95% CI) | Clear cell HR (95% CI) |
|---|---|---|---|---|---|
| Adjustment 1 | |||||
| No hysterectomy | 1.00 (Referent) | 1.00 (Referent) | 1.00 (Referent) | 1.00 (Referent) | 1.00 (Referent) |
| Hysterectomy‡ | 0.98 (0.85 to 1.11) | 1.05 (0.89 to 1.23) | 0.55 (0.28 to 1.06) | 0.69 (0.41 to 1.18) | 0.56 (0.27 to 1.16) |
| Adjustment 2 | |||||
| No hysterectomy | 1.00 (Referent) | 1.00 (Referent) | 1.00 (Referent) | 1.00 (Referent) | 1.00 (Referent) |
| Hysterectomy‡ | 0.65 (0.56 to 0.75) | 0.76 (0.63 to 0.91) | 0.38 (0.19 to 0.75) | 0.30 (0.17 to 0.52) | 0.19 (0.09 to 0.41) |
Time was censored at hysterectomy for malignancy. Hysterectomy is time-varying. Ovarian cancer includes primary ovarian, fallopian tube, and peritoneal cancer. For each histologic subtype analysis, follow-up time is censored at diagnosis of other subtypes. HR = hazard ratio; CI = confidence interval.
Models were stratified by decade of birth and adjusted for age at study entry, tubal ligation (yes/no), and parity (3 or more vs 0–2 births) (Adjustment 1), and additionally endometriosis (yes/no) and fibroids (yes/no) (Adjustment 2). Adjusting for genital prolapse (a third common indication for hysterectomy) did not affect the association between hysterectomy and ovarian cancer, therefore this was not included in presented models.
As hysterectomy is time-varying, the analysis compares exposed time (“hysterectomy,” contributed by women after their hysterectomy) vs unexposed time (“no hysterectomy,” contributed by women before their hysterectomy and by women who did not have a recorded hysterectomy). We assigned date of hysterectomy as date of hospital discharge. For the vast majority (99.9%) of the women in this analysis, admission and discharge dates for hospitalization for hysterectomy were identical (78.9%) or only one month apart (21.0%), because recovery in hospital after hysterectomy is typically short and the provided Hospital Morbidity Data Collection data included admission and discharge month and year (not day).