Table 3.
Association Between Ovulatory Years and Other Reproductive/Hormonal Exposures and Risk of Epithelial Ovarian Cancer, by Histologic Subtype, Among 107,352 Women in the NHS From 1976 to 2006 and 112,632 Women in the NHSII From 1989 to 2005a,b
| All Epithelial (n = 767) |
Serous Invasive (n = 397) |
Endometrioid (n = 118) |
Mucinousc (n = 80) |
P-Heterogeneityd | |||||
| RR | 95% CI | RR | 95% CI | RR | 95% CI | RR | 95% CI | ||
| Ovulatory years (per 1-year increase)e | 1.07 | 1.05, 1.08 | 1.08 | 1.06, 1.10 | 1.08 | 1.05, 1.11 | 1.03 | 1.00, 1.07 | 0.04 |
| Duration of menopause (per 1-year increase) | 1.02 | 1.01, 1.04 | 1.04 | 1.02, 1.06 | 0.96 | 0.93, 0.99 | 1.00 | 0.97, 1.04 | <0.001 |
| Breastfeeding (per 1-year increase)f | 0.80 | 0.71, 0.89 | 0.85 | 0.73, 0.98 | 0.68 | 0.49, 0.94 | 0.45 | 0.27, 0.77 | 0.03 |
| Tubal ligation | 0.69 | 0.55, 0.85 | 0.86 | 0.65, 1.16 | 0.57 | 0.32, 1.00 | 0.51 | 0.25, 1.04 | 0.21 |
| Hysterectomy | 0.69 | 0.52, 0.92 | 0.77 | 0.53, 1.13 | 0.78 | 0.42, 1.44 | 0.57 | 0.23, 1.42 | 0.81 |
| Estrogen use (per 5-year increase)g | 1.36 | 1.13, 1.64 | 1.45 | 1.16, 1.81 | 2.33 | 1.53, 3.53 | 0.93 | 0.38, 2.26 | 0.08 |
Abbreviations: CI, confidence interval; NHS, Nurses’ Health Study; NHSII, Nurses’ Health Study II; RR, incidence rate ratio.
Estimates were adjusted for all variables in the table, plus cohort (NHS or NHSII), parous (yes/no), menopausal status (postmenopause vs. premenopause/perimenopause), and missing data on breastfeeding duration (yes/no) because of noncompletion of questionnaire.
Model excludes women with missing age at natural menopause because of hysterectomy prior to menopause.
Includes borderline and invasive tumors.
P value from likelihood ratio test comparing, for each covariate, the model with separate estimates for the serous invasive, endometrioid, and mucinous histologic subtypes with the model with a single estimate across the 3 subtypes.
Current age (if premenopausal) or age at natural menopause minus (age at menarche + duration of oral contraceptive use in years + parity).
Breastfeeding duration first collected in 1986 in the NHS and 1993 in the NHSII.
Duration of postmenopausal use of unopposed estrogens.