Breast Cancers with Activated Estrogen Receptor More Sensitive to Tamoxifen

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Tamoxifen is a hormonal therapy medicine given to pre- and postmenopausal women to lower the risk of hormone-receptor-positive, early-stage breast cancer coming back (recurrence). Hormonal therapy medicine given after surgery and other treatments (chemotherapy, radiation therapy) is called adjuvant hormonal therapy. Tamoxifen works by blocking the effects of estrogen on breast cancer cells.

A study found that breast cancers with an activated form of estrogen receptor (ER alpha S118-P) benefited from tamoxifen treatment. Breast cancers without this activated form of estrogen receptor didn't benefit from treatment with tamoxifen.

The researchers tested cancer cells from 239 premenopausal women diagnosed with hormone-receptor-positive, early-stage breast cancer to see if the cells had activated estrogen receptors. Just over half (52%) of the cancers had activated hormone receptors. The women were then randomly divided into two groups with no regard for whether the cancers had activated estrogen receptors. Half of the women took tamoxifen for 2 years and the other half did not.

Cancers with the activated form of estrogen receptors that were treated with tamoxifen were 64% less likely to come back (recur) than the same type of cancers not treated with tamoxifen. This large reduction in recurrence seems to be because of the tamoxifen and not due to chance. So tamoxifen treatment significantly lowered the risk of recurrence of cancers with activated estrogen receptors.

Cancers without the activated form of estrogen receptors that were treated with tamoxifen were 13% less likely to come back (recur) than the same type of cancers not treated with tamoxifen. This small reduction in recurrence could possibly be due to chance and not because of the tamoxifen. So tamoxifen treatment didn't significantly lower the risk of recurrence of cancers without activated estrogen receptors.

These results suggest that testing for the activated form of estrogen receptors could help doctors figure out if tamoxifen makes sense for a premenopausal woman diagnosed with hormone-receptor-positive, early-stage breast cancer. This test also might be helpful in planning treatment for postmenopausal women diagnosed with hormone-receptor-positive breast cancer.

While testing breast cancer cells for estrogen receptors is done routinely, testing for the activated form of receptors isn't done routinely right now. More research is needed to figure out if doing this kind of testing could consistently improve treatment for women diagnosed with hormone-receptor-positive, early-stage breast cancer.

Studies like this offer promise for better ways to diagnose and treat breast cancer in the future. Stay tuned to Breastcancer.org for reports on cutting-edge research that moves promise closer to reality.

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