Table 3.
Distribution of invasive breast cancer characteristics in the WHI estrogen plus progestin clinical trial by randomization group*
| Characteristic | Estrogen plus progestin | Placebo | HR of breast cancer (95% CI) |
| No. (%) | No. (%) | ||
| Invasive breast cancer (all) | 385 (100) | 293 (100) | 1.25 (1.07 to 1.46) |
| Histology | |||
| Ductal | 238 (62.1) | 195 (66.6) | 1.16 (0.96 to 1.41) |
| Lobular | 36 (9.4) | 20 (6.8) | 1.63 (0.94 to 2.81) |
| Ductal and lobular | 57 (14.9) | 35 (11.9) | 1.55 (1.02 to 2.37) |
| Tubular | 13 (3.4) | 9 (3.1) | 1.39 (0.59 to 3.25) |
| Other | 39 (10.2) | 34 (11.6) | 1.10 (0.70 to 1.75) |
| Estrogen receptor† | |||
| Positive | 308 (86.5) | 230 (87.5) | 1.27 (1.07 to 1.51) |
| Negative | 48 (13.5) | 33 (12.5) | 1.40 (0.90 to 2.18) |
| Progesterone receptor† | |||
| Positive | 262 (75.2) | 194 (75.7) | 1.29 (1.07 to 1.55) |
| Negative | 86 (24.8) | 62 (24.3) | 1.31 (0.95 to 1.82) |
| ERBB2 (HER2) overexpression† | |||
| Yes | 54 (18.8) | 26 (13.9) | 2.00 (1.25 to 3.19) |
| No | 233 (81.2) | 161 (86.1) | 1.37 (1.12 to 1.68) |
| Triple negative‡ | |||
| Yes | 26 (9.1) | 14 (7.4) | 1.78 (0.93 to 3.41) |
| No | 259 (90.9) | 173 (92.6) | 1.42 (1.17 to 1.72) |
Mean follow-up for analysis was 11.0 years, including 5.6 years of study medication intervention. HRs are from Cox proportional hazards regression models, stratified by age and randomization group in the Women's Health Initiative dietary modification trial. CI = confidence interval; HR = hazard ratio.
The percentage for each category reflects findings from tumors with available information. For example, of tumors with information on estrogen receptor status in the estrogen plus progestin group, 86.5% were positive and 13.5% were negative. Estrogen receptor status missing: 7.5% (estrogen plus progestin) vs 9.9% (placebo); Progesterone receptor status missing: 8.3% (estrogen plus progestin) vs 11.6% (placebo); HER2 status missing: 24.7% (estrogen plus progestin) vs 35.8% (placebo).
Triple negative = estrogen receptor–negative, progesterone receptor–negative, and ERBB2 (HER2) not overexpressed.