The findings, published in the Journal of the American Medical Association, could lead to a partial reversal in how metastatic breast cancer is currently treated using medicines to lower estrogen levels.
"When estrogen-lowering drugs no longer control metastatic breast cancer, the opposite strategy might work," said a statement from the Washington University School of Medicine, which carried out the tests.
Matthew Ellis, an oncologist who was the lead author of the study, said around a third of the women who did not respond to standard treatment reacted well to the new regimen.
"Raising estrogen levels benefited 30 percent of women whose metastatic breast cancer no longer responded to standard anti-estrogen treatment," he said.
Side effects from raising estrogen levels could include headaches, bloating, breast tenderness, fluid retention, nausea and vomiting, but Ellis said side effects were limited in comparison to other treatments.
"We found that estrogen treatment stopped disease progression in many patients and was much better tolerated than chemotherapy would have been."
"Overall, we demonstrated clearly that the low dose was better tolerated than the high dose and was just as effective for controlling metastatic disease."