• Posted February 14, 2024

Scientists Discover New Way to Fight Estrogen-Fueled Breast Cancer

Everyone's heard of fighting fire with fire.

Now that tactic is coming to breast cancer treatment.

Researchers think they've figured out a better way to fight breast cancer fueled by the female hormone estrogen – by employing mechanisms used by the male hormone androgen.

An experimental drug called enobosarm stimulates the androgen receptor on cancer cells, which functions as a tumor suppressor, researchers reported recently in The Lancet Oncology journal.

The drug caused advanced breast cancers to slow or stop in 32% of patients taking a lower dose and 29% of patients taking a higher dose after about six months, phase 2 clinical trial results show.

"Our findings are very promising. They demonstrate that stimulating the androgen receptor pathway with enobosarm can be beneficial,” said senior co-author Dr. Beth Overmoyer, director of the Inflammatory Breast Cancer Program at Dana-Farber Cancer Institute in Boston.

Estrogen receptor-positive (ER+) breast cancers represent up to 80% of all breast cancer cases, researchers said in background notes. Up to now, hormone therapies have focused on suppressing the activity of estrogen in these cases.

These results represent the first advancement in treatment of ER+ breast cancer in decades, researchers said.

“The effectiveness of enobosarm lies in its ability to activate the (androgen receptor) and trigger a natural defense mechanism in breast tissue, thereby slowing the growth of ER+ breast cancer, which relies on the hormone estrogen to grow and spread," said senior co-author Wayne Tilley, director of the Dame Roma Mitchell Cancer Research Laboratories at the University of Adelaide in Australia.

For the phase 2 study, which focuses on safety and potential effectiveness, 136 women with estrogen-positive breast cancer were randomly assigned to take either 9 milligrams or 18 milligrams of enobosarm a day. The drug is taken as a pill.

Results showed that the drug had significant anti-tumor activity and was well-tolerated by patients, researchers said.

Average progression-free survival was 5.6 months in the lower-dose group and 4.2 months in the higher-dose group, results show.

“This is the first time a non-estrogen receptor hormonal treatment approach has been shown to be clinically advantageous in ER+ breast cancer,” Overmoyer said in a university news release.

About 8% of low-dose and 16% of high-dose patients had significant adverse side effects, most often signs of liver damage, elevated calcium levels, and fatigue.

Enobosarm has been granted fast-track designation by the U.S. Food and Drug Administration. The drug will need to undergo a confirmatory phase 3 clinical trial before approval.

More information

The American Cancer Society has more about breast cancer.

SOURCE: University of Adelaide, news release, Feb. 12, 2024