From the article:
Sixty-six postmenopausal women with breast cancer that had spread beyond the breast participated in the study. All participants were originally diagnosed with estrogen receptor positive (ER ) breast tumors, meaning estrogen stimulated tumor growth. Seventy-five percent of breast cancer cases are ER . All participants had received aromatase inhibitor treatment, which severely lowers estrogen levels, but their metastatic tumors had later reappeared or resumed growing.
The study compared a high 30-milligram daily dose of estrogen to a low 6-milligram daily dose, and evaluated how well the treatments controlled the women’s metastatic cancers and how the treatments affected their quality of life. The high dose results in estrogen levels in the blood comparable to that of pregnant women, while the low dose gives estrogen levels similar to that of women who are ovulating, Ellis indicates.
In both the high- and low-dose groups about 30 percent of participants experienced a clinical benefit — their tumors either shrank or stopped growing. Interestingly, the researchers demonstrated that they could predict fairly accurately which patients would have this positive response. They conducted standard positron emission tomography (PET) scans before estrogen treatment and 24 hours later. If metastatic tumors flared, or glowed more brightly, in the PET scans after estrogen was started, they were much more likely to be affected by estrogen therapy. In 80 percent of women with PET flare reactions, tumors responded to estrogen therapy, and in 87 percent of women without PET flares, tumors did not respond to estrogen.
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“The older women in the study were, the fewer estrogen-related symptoms they had,” says Ellis also professor of medicine in the Division of Oncology. “But overall, we demonstrated clearly that the low dose was better tolerated than the high dose and was just as effective for controlling metastatic diseas.”