The Year in Hormones and Cancer Lecture

COMMENTARY: The Year in Hormones and Cancer Lecture: Update of Estrogen plus Progestin Therapy for Menopausal Hormone Replacement Implicating Stem Cells in the Increased Breast Cancer Risk by Kathryn B. Horwitz, Mol Endocrinol 2008(Oct 9) [Epub ahead of print]. [PubMed Abstract]:

This transcript is based on my "The Year in Hormones & Cancer" lecture at ENDO 08 that reviewed current data surrounding hormone replacement therapy (HRT); the relationship between systemic estrogen plus progestin (E+P) treatment and increased breast cancer risk; and explored the hypothesis that women who "develop" breast cancer while on E+P had occult, undiagnosed disease before they started therapy. Beginning with recent HRT data focusing on E+P and its association with breast cancer to set the stage, the lecture then reviewed our newly published data that progestins expand breast cancer stem cells. Finally, the issues of occult or undiagnosed breast cancer in presumably healthy women, and of tumor dormancy in breast cancer survivors, were brought to bear on the discussion. Taken together, these apparently disparate themes allowed me to suggest the idea that systemic progestins have the ability to reawaken cancers that were presumed to be either nonexistent or cured. To avoid this potentially devastating outcome while retaining the benefits of E+P, I advocated the use of local progestin delivery methods, rather than the currently popular systemic routes.

The last two sentences of the "Conclusions" section in the (freely-accessible) PDF version of the full text:

There is considerable evidence for the presence of undetected, possibly undetectable, microdisease in a relatively substantial population of women - both in women who have no evidence of disease, as well as in women who have had breast cancer and are believed to be disease-free. I believe that systemic HRT, especially the progestin component, could be dangerous to such women.