The theoretical risk that gene therapy may cause cancer in humans has hung over the field for decades. Those worries resurfaced last year when a liver tumor was spotted in a patient who had received an experimental treatment for hemophilia from the biotech company UniQure.
But a definitive link between the adeno-associated viruses, or AAVs, that commonly deliver gene therapies and tumor formation has never been established in humans. Though preclinical tests dating back more than 20 years have shown AAVs can slip into the genomes of mice and cause liver cancer, those findings have never been replicated in larger animals or in people.
