An anti-cancer compound in broccoli and cabbage, indole-3-carbinol, is undergoing clinical trials in men with prostate cancer and women with breast cancer because it was found to stop the growth of these cancers in mice.

Now scientists have discovered more about how it works. They’ve found that in breast cancer it lowers the activity of an enzyme associated with rapidly advancing cancer growth, according to a University of California, Berkeley, study appearing this week in the online early edition of Proceedings of the National Academy of Sciences.

The new findings are claimed as the first to explain how indole-3-carbinol (I3C) stops cell growth. This new understanding is expected to speed designs for improved versions of the chemical that would be more effective as a drug and could work against a broader range of breast as well as prostate tumors.