Postmenopausal HRT: What is fact, what is fiction?
What the evidence to date does and does not confirm
HRT may promote, rather than induce, breast cancer
The role of hormones in the etiology of breast cancer is difficult to assess. The Million Women Study49 found that the elevated risk of breast cancer disappeared within 1 year of stopping HRT. This finding implies that hormones may be a promoter, rather than inducer, of neoplasms in the breast.
Breast cancer may be present in many women, but apparent in few
When autopsies were performed on women in their 40s who had died from other diseases, the incidence of breast cancer was 39%, but the clinical detection rate was only 1% for this population.50 This discrepancy suggests that neoplastic cells may be present in the body at any time, but become clinically apparent only under certain conditions.51
More recent data suggest that undifferentiated stem cells in the breast become dysfunctional and result in cancer.52 This theory is supported by the various histologic types of cancer found in the breast.
A weak link
Although it may be compelling to link hormone use with breast cancer, the association is weak and the incidence is lower than in other known relationships such as obesity. At present, the cause of breast neoplasia appears to be multifactorial.
