The Women’s Health Initiative (WHI) enrolled a total of 27,000 predominantly healthy postmenopausal women to assess the risks and benefits of either the use of oral 0.625 mg conjugated estrogens (CE) per day alone or the use of oral 0.625 mg conjugated estrogens plus 2.5 mg medroxyprogesterone acetate (MPA) per day compared to placebo in the prevention of certain chronic diseases. The primary endpoint was the incidence of coronary heart disease (CHD) (nonfatal myocardial infarction and CHD death), with invasive breast cancer as the primary adverse outcome studied. A “global index” included the earliest occurrence of CHD, invasive breast cancer, stroke, pulmonary embolism (PE), endometrial cancer, colorectal cancer, hip fracture, or death due to other cause. The study did not evaluate the effects of CE or CE/MPA on menopausal symptoms.
The CE/MPA substudy was stopped early because, according to the predefined stopping rule, the increased risk of breast cancer and cardiovascular events exceeded the specified benefits included in the “global index.” Results of the CE/MPA substudy, which included 16,608 women (average age of 63 years, range 50 to 79; 83.9% White, 6.5% Black, 5.5% Hispanic), after an average follow-up of 5.2 years are presented in Table 1 below:
Table 1: RELATIVE AND ABSOLUTE RISK SEEN IN THE CE/MPA SUBSTUDY OF WHI
1
Event
2
| Relative Risk CE/MPA vs placebo at 5.2 Years (95% CI
3)
| Placebo n = 8102 | CE/MPA n = 8506 |
| | Absolute Risk per 10,000 Women-Years |
CHD events Non-fatal MI CHD death | 1.29 (1.02 to 1.63) 1.32 (1.02 to 1.72) 1.18 (0.70 to 1.97) | 30 23 6 | 37 30 7 |
Invasive breast cancer
4
| 1.26 (1 to 1.59) | 30 | 38 |
Stroke | 1.41 (1.07 to 1.85) | 21 | 29 |
Pulmonary embolism | 2.13 (1.39 to 3.25) | 8 | 16 |
Colorectal cancer | 0.63 (0.43 to 0.92) | 16 | 10 |
Endometrial cancer | 0.83 (0.47 to 1.47) | 6 | 5 |
Hip fracture | 0.66 (0.45 to 0.98) | 15 | 10 |
Death due to causes other than the events above | 0.92 (0.74 to 1.14) | 40 | 37 |
Global Index
2
| 1.15 (1.03 to 1.28) | 151 | 170 |
Deep vein thrombosis
5
| 2.07 (1.49 to 2.87) | 13 | 26 |
Vertebral fractures
5
| 0.66 (0.44 to 0.98) | 15 | 9 |
Other osteoporotic fractures
5
| 0.77 (0.69 to 0.86) | 170 | 131 |
1 adapted from JAMA, 2002; 288:321-333
2 a subset of the events was combined in a “global index”, defined as the earliest occurrence of CHD events, invasive breast cancer, stroke, pulmonary embolism, endometrial cancer, colorectal cancer, hip fracture, or death due to other causes
3 nominal confidence intervals unadjusted for multiple looks and multiple comparisons
4 includes metastatic and non-metastatic breast cancer with the exception of in situ breast cancer
5 not included in Global Index
For those outcomes included in the “global index,” the absolute excess risks per 10,000 women-years in the group treated with CE/MPA were 7 more CHD events, 8 more strokes, 8 more PEs, and 8 more invasive breast cancers, while the absolute risk reductions per 10,000 women-years were 6 fewer colorectal cancers and 5 fewer hip fractures. The absolute excess risk of events included in the “global index” was 19 per 10,000 women-years. There was no difference between the groups in terms of all-cause mortality (See
BOXED WARNINGS,
WARNINGS, and
PRECAUTIONS).