There've been reports like this about quercetin (a flavonoid found naturally in fruits and vegetables) dating back to the '70s. However, effects in the test tube don't mean that the supplement causes a problem in human use:

"Most of the results of in vivo studies (in live animals) indicate that quercetin is not carcinogenic. Since 1969, the International Agency for Research on Cancer (IARC) has undertaken a program to evaluate the carcinogenic risk of chemicals. In 1999, IARC concluded that quercetin is not classified carcinogenic to humans. In the U.S. and Europe, supplements of quercetin is commercially available, and beneficial effects of quercetin supplements were reported in clinical trials. Overall, quercetin is genotoxic to salmonella, but its safety upon human application is approved."

The Ames test provides one measure to assess safety of compounds, but it has limitations. And not everything that passes the Ames test is guaranteed safe.

Here is a link that might be useful: Quercetin and safety

Quercetin, quercetrin, and related compounds are present in many fruits and vegetables (apples and onions are two notable examples). Fruits and vegetables are generally a more economic way of getting querc, and they provide other important phytochemicals. But if you are taking it to supplement a balanced diet for a particular reason, there is no evidence I am aware of that it is harmful.

I used this for 2 months. It didn't do any appreciable thing.