Breast Cancer Biomarker May ID Tamoxifen Responders


An international team of researchers have uncovered a breast cancer biomarker that may help clinicians identify which women will respond to tamoxifen, a widely used drug for patients with estrogen receptor-positive breast cancer. Currently, the drug is ineffective in up to one-third of women who take it.

Identifying tamoxifen responders could save lives

Tamoxifen interferes with the activity of estrogen, a hormone that can promote the development of breast cancer. The drug has been used for more than three decades to treat breast cancer, and for about 10 years to reduce the risk of breast cancer in women who are at high risk for the disease.

Investigators at the Kimmel Cancer Center at Thomas Jefferson University, along with collaborators from around the world, evaluated the levels of a biomarker called Stat5 in 1,022 women in five archival cohorts of breast cancer. They discovered that women whose breast cancer tumors retained the active form of Stat5 were more likely to respond to tamoxifen.


Among women treated with tamoxifen who do not have active Stat5, however, there was up to a 20-fold increased risk of dying from breast cancer. The authors also discovered that Stat5 disappeared in most of the more aggressive tumors and when the cancer spread to the lymph nodes.

Stat5 is a protein that regulates expression of certain genes. In pregnant women the protein is activated by the hormone prolactin and triggers milk production. Lower levels of active Stat5 are also found in healthy breast tissue of nonpregnant women.

Amy Peck, PhD, and the study’s lead author, pointed out that “we are optimistic about the utility of Stat5 as a biomarker.” One advantage of optimizing the biomarker Stat5 is that the test is inexpensive, simple, and can easily be integrated into routine analysis in pathology labs.

The findings of this study are significant because, according to Hallgeir Rui, MD, PhD, professor of oncology at Kimmel, “Identification of predictive biomarkers present in breast cancer will lead to improved individualized therapies tailored specifically towards each woman’s cancer.” Women who don’t have active Stat5 may then be offered treatment options other than tamoxifen.

Peck AR et al. Journal of Clinical Oncology 2011 May 16; doi: 10.1200/JCO.2010.30.3552