Well, it's part of the cancer process; most cancers couldn't survive without it. But that's also true of, for example, local production of DNA, or anaerobic glycolysis, or angioneogenesis.
It's not true that if you expose tissues to lots of H₂O₂ they'll get cancer.
It's not true that if you expose tissues to lots of H₂O₂ they'll get cancer.