In 1980, quercetin was reported to induce cancer in animals.4 Most further research did not find this to be true, however.5 6 While quercetin is mutagenic in test tube studies, it does not appear to be mutagenic in animal studies.7 In fact, quercetin has been found to inhibit both tumor promoters8 and human cancer cells.9 People who eat high levels of flavonoids have been found to have an overall lower risk of getting a wide variety of cancers,10 though preliminary human research studying only foods high in quercetin has found no relation to cancer risk one way or the other.11 Despite the confusion, in recent years experts have shifted their view of quercetin from concerns that it might cause cancer in test tube studies to guarded hope that quercetin has anticancer effects in humans.12
Please note of course that True Star Health does happen to be a marketer of Quercetin among other things, so there's is no guarantee that they, like most marketers, may very well tell you it'll slice, dice and defeat evil emporers, if it'll get you to buy it.

But at first glance I see no plain or bold references to Quercetin being carcinogenic.
Hope this helps.
Kev
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