The biochemist I raised and who is sitting next to me drinking beers I paid for so that he would not drink all my expensive whiskey says that ethidium bromide doesn't even pass the Ames test except with liver homogenates, and its actual carcinogenicity is unproven. Your body produces similar carbon rings --- phenylalanines --- constantly. You can't simply derive carcinogencity axiomatically.

(I'm butchering this and mostly just having fun with it.)

Edit

He is correcting me and saying that at the moment he is technically working as a veterinary immunologist. But the point about 6-carbon thingies stands.