New research indicates that anti-estrogen drugs that decrease tumor growth in women with estrogen receptor–positive (ER+) breast cancer also increase the activity of breast cancer stem cells by activating the Notch signaling pathway (Simões BM et al. Cell Rep. doi:10.1016/j.celrep.2015.08.050 [published online September 17, 2015]).
In studies conducted with patient-derived breast cancers in mice and cell culture, investigators at the University of Manchester, in the United Kingdom, found an association between the presence of the NOTCH4 receptor and resistance of cancer stem cells to anti-estrogen treatment. In tumors taken from patients before treatment, elevated expression of NOTCH genes was linked to breast cancer metastasis and poor survival.
Hampton T. Tackling Breast Cancers Resistant to Hormone Therapy. JAMA. 2015;314(17):1788. doi:10.1001/jama.2015.13935