A new study has moved forward with a drug that could target a newly-identified breast cancer driver. Breast cancers are defined and treated according to their hormonal drivers, of which the most common are estrogen, progesterone, and HER2. Androgen receptors have now been targeted as a potential driver of so-called triple negative breast cancers.

The new clinical trial has demonstrated that blocking the androgen receptor could stop the growth of some triple negative breast cancers. Currently, chemotherapy, radiation, and surgery have been the only treatments for these aggressive types of breast cancer.

“This work is a concise example of modern cancer science in action. We noticed something in the clinic, worked on it in the lab, and now are happy to report the lab work is once again back in the clinic where it has the very real potential to benefit patients,” said Dr. Anthony Elias breast cancer program director at the University of Colorado Cancer Center.

Androgens, such as testosterone, are already known to drive prostate cancer. This means drugs targeting androgen receptors and cancer cells’ ability to use the hormone already exist. Researchers have been experimenting with experimental androgen-blocking medications on triple negative breast cancers since 2001. Now, a phase I clinical trial that has demonstrated the safety of a drug known as enzalutamide is expected to become a phase II trial and begin demonstrating results.

“Normally, the way these hormones work is by attaching to receptors in the cell cytoplasm, at which point the receptor draws itself and the hormone molecule inside the nucleus where it regulates genes,” said Dr. Jennifer Richer, co-director of the CU Cancer Center Tissue Processing and Procurement Core.

Enzalutamide, which was recently approved by the U.S. Food and Drug Administration for use with prostate cancer, stops androgen receptors from entering a cell’s nucleus.

“Interestingly, it seems that estrogen-positive breast cancers are susceptible to the same drug,” said Richer.