Washington, DCPhysicians who treat women with the breast cancer susceptibility gene BRCA1 often remove their patients ovaries to eliminate the source of estrogen they believe fuels cancer growth. Yet they also know that anti-estrogen therapies don't work to treat breast or ovarian cancer that might develop. That paradox has led scientists to question exactly how, or if, estrogen is involved in cancer development and whether removal of ovaries makes sense.
Now, a team of researchers from Georgetown Universitys Lombardi Comprehensive Cancer Center have shed light on the mechanism that makes ovary removal protective against tumor development in this unique population. They discovered that estrogen is needed to start the cancer process, but then the BRCA1 mutations somehow render the new tumors unresponsive to estrogen, producing cancer that is more aggressive and difficult to treat.
In a study published electronically on July 23 in the journal Oncogene, Georgetown researchers found that mutations of the BRCA1 gene can cause the estrogen-signaling pathway to go awry after cancer starts to grow. The mutated gene somehow causes the tumor cells to stop expressing the estrogen receptor, a protein that sits on the surface of the cell and recognizes the presence of the hormone. This means that these cancers lose sensitivity to estrogen (and potent anti-estrogen therapies like Tamoxifen) after tumors begin to form.
To show that estrogen was involved in the initiation of the cancer, the researchers overexpressed the estrogen receptor in a laboratory mouse model with a BRCA1 mutation and a p53 gene mutation (the two gene mutations usually coexist in human cancer). As predicted, they found that when exposed to estrogen, these mice developed cancerous tumors.
Estrogen is definitely necessary for these tumors to develop, but somewhere along the tumor development pathway, the emerging tumors lose their sensitivity to estrogen, said Priscilla
|Contact: Becky Wexler|
Georgetown University Medical Center