Benzene is both, toxic and carcinogenic (cancer causing).
In fact, it might be considered “the mother of all carcinogens” as a large number of carcinogens have structures that include benzene rings.
In liver, benzene is oxidized to an epoxide and benzopyrene is converted into an epoxy diol. These substances are carcinogenic and can react with DNA and thus, can induce mutation leading to uncontrolled growth of cancer cells.