Alternating Estrogen Stimulation And Estrogen Blocking May Be Effective for Metastatic Breast Cancer

Estrogen-receptor positive (ER+) breast cancer involves cancer cells with receptors that attach to the hormone estrogen. With this form of the disease, drugs that block the estrogen receptor are commonly used as treatment. Researchers at Dartmouth Cancer Center, though, say that estrogens that simulate the receptor can also work. This led them to conduct a clinical trial aimed at seeing if alternating between these treatments was beneficial.

The cancer center recently shared the findings of a Phase II clinical trial implementing this treatment approach. It was published in the journal Clinical Cancer Research. In the POLLY trial, as it was called, the team recruited post-menopausal women with metastatic ER+ breast cancer and switched between estrogen stimulation for a period of eight weeks and estrogen deprivation for a period of 16 weeks, keeping this schedule until disease progression.

Of the 19 patients enrolled, three saw tumor shrinkage during the treatment and five had disease stabilization for at least 24 weeks. That means that 42% of the trial participants benefitted. After cancer progressed on this treatment, 12 patients chose to receive non-cycling treatment with one drug, five of which – again, 42% – had disease stabilization for at least another 24 weeks.

For those who benefitted, researchers also found something that may be helpful for use of this possible treatment.

Dr. Todd W. Miller, study co-author and cancer researcher, says, “Tumor features called biomarkers that predict which patients will benefit from estrogen therapy have also not been reported. In the POLLY trial, we found that mutations in the gene encoding ER, which often arise in tumors that become resistant to anti-estrogen drugs, were present in tumors from the only two patients whose tumors shrank in response to estrogen therapy within the first 8 weeks. This suggests that ER mutations may be useful in identifying patients who are likely to benefit from this treatment strategy.”

The researchers plan to learn more about this in a follow-up clinical study, which will investigate the effectiveness of estrogen therapy in patients with or without tumor mutations in ER.

If you’d like to read the entire findings of the POLLY trial, click here.