Study finds estrogen can trick breast-cancer tumors

ST. LOUIS – Estrogen is medicine’s most two-faced hormone, confusing doctors and patients for decades on its role in the benefits and risks of heart disease and cancer.

Now researchers at Washington University have shown that in some women with breast cancer tumors that thrive on the hormone, giving them more estrogen can actually trick the tumors into submission. Estrogen therapy could be used to treat women with certain kinds of breast cancer, an attractive alternative to chemotherapy.

In a study of 66 women with metastatic breast cancer, Dr. Matthew Ellis and colleagues found that tumors in one-third of the women stopped growing or shrank after estrogen therapy. The women initially were given estrogen-lowering drugs, but had developed a resistance to them. They were then put on daily estrogen pills.

Ellis, an associate professor of medicine, presented the findings Thursday at the San Antonio Breast Cancer Symposium. “Estrogen-dependent cancers love to grow on estrogen,” he said. “When you take it away they forage around looking for alternative ways to grow. … Now you have a breast cancer that used to like estrogen, now is growing in response to some other stimuli and you shock it by giving it back estrogen.”