Therapeutic Estradiol for Breast Cancer

This trial tests whether estradiol, a form of estrogen, can help treat ER beta positive, triple negative breast cancer. This cancer lacks certain hormone receptors but may have an excess of a receptor called ER beta. The study aims to determine if estradiol can slow or shrink these tumors. Women with this type of breast cancer, who have experienced its spread to nearby tissues or beyond and have undergone up to three chemotherapy regimens, might be suitable candidates. As a Phase 2 trial, this research focuses on measuring the treatment's effectiveness in an initial, smaller group of participants.

The trial requires participants to stop using strong inducers or inhibitors of CYP3A4 before registration. Additionally, no chemotherapy, immunotherapy, biologic therapy, hormonal therapy, monoclonal antibodies, or targeted therapies are allowed within 14 days prior to registration.

Research has shown that estradiol, a type of estrogen, is likely safe for treating breast cancer. Studies have found that vaginal estrogen therapy does not increase the risk of early death from breast cancer. This is encouraging for breast cancer survivors, suggesting estradiol could be a safe option.

Other studies indicate that local estrogen therapy does not raise the chance of cancer returning or increase death rates in people taking tamoxifen, a common breast cancer medication. This provides more evidence that estradiol is well-tolerated.

Most treatments for breast cancer involve chemotherapy, targeted therapy, or hormone therapy that lowers estrogen levels. But estradiol works differently, as it is a form of estrogen itself. Researchers are excited because estradiol aims to exploit a unique vulnerability in some breast cancers that become resistant to standard treatments. This approach could offer a new pathway for patients whose cancers no longer respond to conventional therapies.

Research has shown that estradiol, a type of estrogen, might slow the growth of certain breast cancer cells. In lab studies, cancer cells with high levels of a specific hormone receptor called ER beta grew more slowly when exposed to estrogen. This finding is significant because some triple-negative breast cancers, which lack other hormone receptors, still have high ER beta levels. Estradiol, which participants in this trial will receive, could potentially shrink these tumors by interacting with ER beta. Although studies on vaginal estrogen use showed no increased risk of breast cancer recurrence, the exact effect of estradiol on this specific cancer type remains under investigation.¹²³⁵⁶