FRIDAY, Dec. 13, 2024 (HealthDay News) -- An experimental hormone therapy pill has shown promise in extending the lives of women with tough-to-treat advanced breast cancer, a new clinical trial shows.

The drug, imlunestrant, improved progression-free survival in patients whose breast cancer was driven by the female hormone estrogen.

The drug was particularly effective in breast cancers with a mutation in the ESR1 gene, which encodes estrogen receptors, according to results published Dec. 11 in the New England Journal of Medicine. Researchers also presented the findings simultaneously at the San Antonio Breast Cancer Symposium.

“These promising results mean that imlunestrant is potentially another single-agent option for the many patients whose recurrent breast cancers harbor ESR1 mutations,” said researcher Dr. Komal Jhaveri, section head of the Endocrine Therapy Research Group at Memorial Sloan Kettering Cancer Center in New York City.

Imlunestrant is a selective estrogen receptor degrader (SERD), which works by causing the estrogen receptors in breast cancer cells to become less responsive to the female hormone.

For the clinical trial, researchers recruited 874 women with advanced breast cancer that had either come back or progressed despite treatment.

Their cancers were all estrogen receptor (ER)-positive, meaning that their growth was fueled by the hormone. About 70% of all breast cancers are ER-positive, according to the Cleveland Clinic.

One-third of the women were randomly assigned to receive imlunestrant, and another third to receive imlunestrant alongside the targeted therapy drug Verzenio (abemaciclib). The remaining third received standard hormone therapy.

Verzenio is a CDK4/6 inhibitor, which fights breast cancer by interrupting the process through which breast cancer cells divide and multiply.

In women with ESR1 mutations, imlunestrant reduced the risk of cancer progression or death by 38% compared with standard hormone therapy.

Imlunestrant worked even more effectively when combined with Verzenio, researchers added. That combination reduced risk of progression or death by 43%.

All told, women who got the combination therapy had a median progression-free survival of 9.4 months, compared with 5.5 months for imlunestrant alone and 3.8 months for standard therapy.

The combination therapy also proved safe, with only about 6% of women needing to stop taking the drug due to side effects, researchers said.

Both imlunestrant and Verzenio are taken as pills, researchers noted. Imlunestrant also can slip past the blood-brain barrier, potentially helping treat breast cancers that have spread to the brain.

“Taken together, these data are encouraging for patients and show that imlunestrant, as monotherapy or combined with abemaciclib, could provide an all-oral targeted therapy option after progression on endocrine therapy for patients with ER-positive, HER2-negative advanced breast cancer,” Jhaveri said in a meeting news release.

The study was funded by Eli Lilly and Co., the developer of imlunestrant.

More information

The American Cancer Society has more on hormone-driven breast cancers.

SOURCE: San Antonio Breast Cancer Symposium, news release, Dec. 11, 2024