Table 3. Associations between oestrogen plus progestin therapy only and ovarian cancer among 68 596 women with an intact uteri at baseline, NIH-AARP Diet and Health Study Cohort, 1995–2006.
| Numbers of cancers | Person-years | RRa (95% CI) | P -value b | |
|---|---|---|---|---|
| No MHT use | 150 | 316 239 | 1.00 (reference) | |
| EPT only | 98 | 170 556 | 1.43 (1.09, 1.86) | |
| Duration of EPT only use (years) | ||||
| <10 | 67 | 126 465 | 1.33 (0.98, 1.79) | 0.26 |
| ⩾ 10 | 31 | 43 752 | 1.68 (1.13, 2.49) | |
| Progestin dose c | ||||
| <1 mg | 2 | 5854 | 0.83 (0.21, 3.36) | 0.15 |
| 2.5 mg | 49 | 85 828 | 1.35 (0.98, 1.86) | |
| 5 mg | 16 | 23 968 | 1.60 (0.95, 2.68) | |
| 10 mg | 13 | 19 792 | 1.58 (0.90, 2.79) | |
| Days on progestin per month c | ||||
| <10 | 10 | 17 482 | 1.41 (0.74, 2.69) | 0.70 |
| 10–14 | 26 | 39 150 | 1.69 (1.10, 2.58) | |
| 15–19 | 2 | 3300 | 1.48 (0.37, 6.00) | |
| 20–25 | 11 | 17 499 | 1.51 (0.81, 2.79) | |
| Daily | 48 | 83 396 | 1.43 (1.03, 2.01) | |
| Regimen of EPT only use d | ||||
| Sequential | 36 | 56 632 | 1.60 (1.10, 2.33) | |
| Continuous | 48 | 83 396 | 1.43 (1.03, 2.01) | |
| Regimen and duration of EPT only use | ||||
| Sequential | ||||
| <10 years | 26 | 37 417 | 1.81 (1.18, 2.78) | 0.10 |
| ⩾10 years | 9 | 18 840 | 1.13 (0.57, 2.23) | |
| Continuous | ||||
| <10 years | 36 | 66 345 | 1.37 (0.94, 1.99) | 0.03 |
| ⩾10 years | 12 | 16 737 | 1.72 (0.95, 3.11) | |
Abbreviations: CI=confidence interval; EPT=oestrogen plus progestin therapy; ET=unopposed oestrogen therapy; MHT=menopausal hormone therapy; NIH-AARP=National Institutes of Health-AARP; RR=hazard rate ratio.
RR adjusted for continuous age (years), race (white, other/unknown), parity (nulliparous, 1, 2, 3+, unknown), duration of oral contraceptive use (none, <10 years, ⩾10 years, or unknown), and body mass index (<25, 25–29, ⩾30 kg m−2, or unknown); models included terms for use of other MHT formulations (ET only, other formulations, or unknown).
P-values (two-sided) for trend were calculated using ordinal (duration, progestin dose, days on progestin per month, regimen and duration) variables based on the categories and referent group shown.
Cases do not add to total because of missing values (n=18 missing progestin dose and n=1 missing days on progestin per month).
Sequential regimen usage was defined as oestrogen with <15 days progestin per month and the continuous regimen usage as oestrogen with ‘daily’ use of progestin (>25 days progestin per month). The usage pattern that included 15–25 days per month was modelled as a separate parameter in the statistical model (results not shown).