The fish that didn't respond well to I3C were given huge amounts-far in excess of what a person would, or could, take on a daily basis. At these huge amounts, I3C appeared to promote, rather than impede, cancer that had already been generated by cancer-causing chemicals. If the fish were given I3C before or during cancer-causing chemicals, I3C protected them against cancer. It was only if huge amounts were given after cancer was in progress that problems occurred. From a scientific standpoint, these studies have little or no relevance to humans since fish metabolize chemicals very differently than humans.
Rodents are a much better model for humans.
In rodent studies, I3C inhibits cancer and stops DNA damage. Humans are the best model yet. In human studies, I3C neutralizes estrogen, reducing it to a less powerful form. In studies on human breast cancer cells, I3C works better than tamoxifen to stop growth. And in a test of 90 different potential cancer inhibitors, I3C scored at the very top.