Table 3.
Association between duration of OC use and ovarian cancer risk among Nurses’ Health Study II participants (1989-2013)
| Model 1a | Model 2b | Model 3c | ||||||
|---|---|---|---|---|---|---|---|---|
| Cases | Person-yrs | HR | 95% CI | HR | 95% CI | HR | 95% CI | |
| Duration of OC use | ||||||||
| Never | 36 | 321,519 | 1.00 | (Ref). | 1.00 | (Ref). | 1.00 | (Ref). |
| ≤6 months | 33 | 165,347 | 1.65 | (1.02, 2.64) | 1.78 | (1.10, 2.85) | 1.82 | (1.13, 2.93) |
| ≥6 months – 1 year | 25 | 159,328 | 1.36 | (0.82, 2.27) | 1.46 | (0.87, 2.44) | 1.51 | (0.90, 2.53) |
| >1-<5 years | 96 | 679,339 | 1.19 | (0.81, 1.75) | 1.29 | (0.88, 1.90) | 1.33 | (0.90, 1.97) |
| 5-<10 years | 59 | 551,456 | 0.95 | (0.63, 1.44) | 0.98 | (0.65, 1.49) | 1.03 | (0.67, 1.56) |
| 10-<15 years | 26 | 207,436 | 1.10 | (0.66, 1.83) | 1.06 | (0.63, 1.76) | 1.11 | (0.66, 1.84) |
| ≥15 years | 6 | 94,253 | 0.47 | (0.20, 1.11) | 0.40 | (0.17, 0.96) | 0.43 | (0.18, 1.04) |
| p-trendd | 0.02 | 0.003 | 0.006 | |||||
| p-trende | 0.003 | 0.0003 | 0.0005 | |||||
a
Adjusted for age (years) and calendar time
b
Adjusted for Model 1 variables + tubal ligation (yes/no), parity (number of pregnancies), breastfeeding duration (months), and missing breastfeeding duration, laparoscopically-confirmed endometriosis (ever/never)
c
Adjusted for Model 2 variables + body mass index (kg/m2)
d
P-trend is calculated including the never OC users
e
P-trend is calculated among ever OC users