Estrogen curbs breast cancer aggressiveness

Kathleen Blanchard's picture
Breast cancer stem cells

Estrogen has been found to reduce the number of breast cancer stem cells, opening the doors for new treatment options.

Researchers say chemotherapy and radiation shrink cancer tumors, but do little to eliminate breast cancer stem cells. The new findings that estrogen can lower the number of stem cells means a potential breast cancer cure.

María Vivanco who led the research says, “To our surprise, what we have seen is that estrogen reduces the proportion of breast stem cells which means a mechanism for explaining this better prognosis observed with tumours that express the estrogen receptor. That is, those tumours expressing the estrogen receptor are less aggressive, better differentiated and thus have a better prognosis”

Cancer stem cells are responsible for initiating tumors, making the findings especially important. The findings also adds to other advances in breast cancer surveillance and survival.


Estrogen is important for breast development. It also is known to promote breast cancer. Until now researchers new nothing about the hormone's role in curbing the number of breast cancer stem cells.

The researchers note the findings help explain a number of observations related to breast cancer that include the high levels of estrogen found in postmenopausal women diagnosed with the disease that is also associated with less aggressive tumors.

They also say understanding that estrogen reduces the proportion of breast cancer stem cells helps explain why pregnancy and lactation has a protective effect. Absence of estrogen receptors is associated with more aggressive tumors and poorer rates of survival.

Basque Research