Estrogen Shrinks Tumors Refractory to Antiestrogen Therapy

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As Reported by HealthDay News. 2009 Aug 18


A new study has found that estrogen can shrink some breast cancer tumors—a finding that contradicts the conventional practice of treating breast cancer with antiestrogen therapy such as tamoxifen and aromatase inhibitors. The tumors that responded had become resistant to antiestrogen therapy. Some of these tumors shrank when treated with estrogen, while for others, the estrogen exposure resensitized them to antiestrogen treatment. The study investigators were surprised by the findings. Since this was a preliminary study, they recommended that larger trials be conducted. The mechanism for the paradoxical response is not yet understood. Using estrogen in the treatment of breast cancer was standard practice before the era of antiestrogen therapy. The present findings confirm the earlier experience that metastatic hormone-dependent breast cancer in postmenopausal women can be treated with estrogen. The new findings also suggest that estrogen therapy might be reinstituted after antiestrogen therapy fails, but at lower doses. To test that hypothesis, the investigators studied 66 women with estrogen-positive tumors that had been previously treated with aromatase inhibitors. The women were given either 6 or 30 mg of estradiol per day. Regardless of the dose, tumors shrank in 30% of the women, although adverse effects were less common with the lower dose. Some of the women whose tumors later recurred again responded to aromatase inhibitors. The investigators are attempting to determine which subgroups of patients would benefit from the estrogen protocol. The research results were reported in the August 19 issue of the Journal of the American Medical Association.

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