Dive Brief:

• Nine people with spinal muscular atrophy who received Novartis’ gene therapy Zolgensma later developed tumors, and two cases displayed evidence that the virus used to deliver the treatment fused itself into patient DNA, the Swiss drugmaker said Thursday.
• Novartis issued its statement in response to circulating reports of the cancer cases from prominent SMA patient organizations. One such group, SMA Europe, called on the company to provide “clear, reliable and understandable information.”
• Novartis said it notified health authorities after each case and “will continue to work with them on next steps.” The theoretical risk that the adeno-associated virus, or AAV, used in Zolgensma might integrate into a patient’s DNA is listed among the warnings on the therapy’s prescribing information. The likelihood that treatment could pose a cancer risk has also been a long-held fear in gene therapy research.

Dive Insight:

Zolgensma is one of several drugs that in the last decade have launched and transformed treatment of SMA. Before these drugs came along, SMA was, in its most severe form, fatal for many young children and the cause of lifelong disability for older patients with milder versions. Yet Zolgensma and other therapies from Biogen, Roche and more recently Scholar Rock have shown the ability to help change the disease’s course.

As a genetic disease, SMA was a ripe opportunity for a treatment that could replace the faulty or missing gene driving the condition. Zolgensma, developed by the biotech AveXis — which Novartis later acquired — provides that solution by stimulating production of a protein called SMN that’s deficient in people with SMA. It does so by packaging into an AAV a gene encoding for that protein, which is then expressed when delivered into cells.

Initially approved for people under two years of age and given a $2 billion-plus price tag, Zolgensma encountered some early adversity on the market amid a Food and Drug Administration probe into data used to support its clearance. But Novartis was eventually cleared of any wrongdoing, and later won a hard-fought approval enabling broader use of Zolgensma.

Along the way, Zolgensma has become the most commercially successful gene replacement therapy, recording more than $1 billion last year and $1.1 billion through the first nine months of 2026. Novartis said in its statement Thursday that 6,000 people have now received Zolgensma. Other gene therapies with high sales expectations, like Sarepta Therapeutics’ Elevidys for Duchenne muscular dystrophy, have sputtered. And BioMarin Pharmaceutical withdrew from market its hemophilia treatment Roctavian because of slow adoption.

Still, the potential that a treatment like Zolgensma might errantly lead to cancer has worried gene therapy researchers and regulators for years. Research dating back decades has indicated that AAVs can integrate into the genomes of certain animals, and concerns whether the same situation might occur in humans grew after the recipient of a gene therapy from UniQure developed liver cancer in 2021.

UniQure’s treatment was later exonerated, but the issue of cancer risk was then prominently featured at an FDA meeting that year where researchers called for greater monitoring. Two reports of cancer in Zolgensma recipients later emerged in case reports in 2023 and 2025, respectively, though the treatment wasn’t definitively linked to those occurrences in either instance.

The new disclosure confirms that seven more cases have occurred since then, two of which involved instances of DNA integration. Novartis said that in both of those cases, the patients were treated and continue to be monitored.

Patient groups are now searching for answers. Circulating reports of cancer are “deeply concerning for families, particularly for parents whose children have already received Zolgensma or who are currently considering treatment,” SMA Europe said in a statement.

“Families need clear, reliable and understandable information and should not be left to piece together a potential safety concern from social media, rumours or incomplete reports,” the organization said. “We have strongly urged the company to provide clear information on what is currently known, what remains uncertain, what this may mean for people who have already received treatment, and whether any additional monitoring or action is recommended.”

In the U.S., another patient group, Cure SMA, noted that three of the nine patients have had their tumors tested. One of those cases appears unrelated to Zolgensma.

“We are taking these reports seriously, and we are committed to sharing clear, accurate information with our community as soon as it becomes available,” the group said in a statement. “Cure SMA has reached out to Novartis, and we are reviewing available safety information with clinical and scientific experts while remaining in contact with regulators and our clinical partners.”