HRT and breast cancer risk: a realistic perspective

A new analysis from the Women's Health Initiative included data on breast cancer incidence over a 11-year period from the randomized trial of conjugated equine estrogens (CEE) plus medroxyprogesterone acetate (MPA) and a subsequent observational follow-up. The conclusions were that CEE/MPA use was associated with an increase in both breast cancer incidence and mortality. We have concerns over the validity of their statistical analyses, as adjustments for baseline characteristics or for multiple comparisons demonstrate no significant differences in incidence between those allocated to CEE/MPA or placebo. We suspect that the apparent increase in mortality is the result of surveillance and detection bias rather than a true cause and effect. Even if such an effect were true, mortality from breast cancer would still be a very rare event. We also question the clinical relevance and applicability of their findings. The data over the 11 years show no increased risk of breast cancer with CEE/MPA in women who had not previously used hormone replacement therapy (HRT), and the vast majority of women on HRT would not be prior users at initiation. It should be remembered that women using CEE alone showed a significant decrease in breast cancer risk in the WHI trial and follow-up. Even if combined estrogen?progestogen HRT did cause an increase in breast cancer risk, and this is not proven, the magnitude of that risk is small, and less than that risk seen with many lifestyle factors. HRT is a benefit, not a risk, for those women requiring it.