The US Food and Drug Administration is investigating a serious risk of cancer linked to Zolgensma, Novartis's one-time gene therapy for spinal muscular atrophy, after finding evidence that the treatment's DNA had inserted itself into the genetic code of children who later developed tumours. The agency said on Friday, November 6, that it had received postmarketing reports of malignancies in treated children, including confirmed cases of insertional oncogenesis involving the GLI1 gene. It is the first confirmation that the therapy's vector DNA integrated into patients' DNA and was linked to tumour formation.

Key Points

• The FDA announced on November 6, 2026, that it is investigating a serious risk of malignancy linked to Zolgensma, Novartis's gene therapy for spinal muscular atrophy in children under two.
• Three cases involved tumours linked to the GLI1 oncogene. In two, molecular analysis confirmed Zolgensma's AAV vector DNA had integrated into the patients' genome, with the treatment's promoter inserted within GLI1.
• Tumours were reported in the central and peripheral nervous systems, spinal and paraspinal regions, and the kidney. Novartis has received nine tumour reports since approval in May 2019, and the therapy has been given to more than 6,000 children.
• The FDA says the same risk applies to Itvisma, for patients aged two and older, because both use the same vector and construct; no tumour cases have been reported after Itvisma to date.
• The agency says the benefits of both products continue to outweigh their risks, but it is evaluating whether regulatory action is appropriate and whether the label and follow-up studies are adequate.

What Happened

On Friday, November 6, 2026, the FDA said it had received postmarketing reports of malignancies in patients treated with Zolgensma, an adeno-associated virus (AAV) vector-based gene therapy, including confirmed cases of insertional oncogenesis involving GLI1, a gene that can cause cancer when overexpressed.

In two cases, molecular analysis of tumour tissue showed Zolgensma's AAV vector DNA had integrated into the host genome, with the treatment's promoter inserted within GLI1. In the third GLI1 case, the mechanism remains under investigation. The FDA also cited two published reports of AAV integration-driven oncogenesis in other programmes.

Novartis disclosed earlier on Friday that two cases showed evidence of being linked to its gene therapy, and said it had received nine tumour reports in total since Zolgensma was first approved in the United States in May 2019.

Background: Zolgensma and Spinal Muscular Atrophy

Spinal muscular atrophy (SMA) is a rare genetic disorder in which the loss of motor neurons progressively weakens the muscles, leaving many affected babies unable to sit, stand or swallow. It is caused by a faulty SMN1 gene, and without treatment the most severe form is often fatal in early childhood. Zolgensma uses a modified virus to deliver a working copy of SMN1 into the patient's cells in one intravenous infusion.

Zolgensma was first approved in the United States on May 24, 2019, for children under two. Novartis later developed Itvisma, which uses the same vector and construct but is injected into the spinal fluid for patients aged two and older, first approved on November 24, 2025.

Zolgensma Tumour Risk: What the Evidence Shows

The central finding is insertional oncogenesis: genetic material carried by the therapy inserted itself into the patient's own DNA at or near a cancer-causing gene, and the treatment's promoter appears to have switched that gene on. GLI1 is a known oncogene, and when overexpressed it can drive uncontrolled cell growth, the mechanism the FDA says it has now confirmed in two children.

The finding matters because the current US prescribing information for both products describes only a "theoretical risk of tumorigenicity due to integration of AAV vector DNA into the genome". AAV vectors were long regarded as carrying a very low integration risk. The FDA's announcement shows that, in rare cases, integration does happen. The agency is now evaluating whether the label and Novartis's long-term follow-up studies are adequate.

Reactions and Quotes

The FDA struck a balance, confirming the seriousness of the findings while urging families not to abandon treatment. "The overall benefits of Zolgensma and Itvisma continue to outweigh their potential risks for their approved uses," the agency said.

Novartis said it had notified health authorities "in a timely and appropriate manner" in both cases and that the potential tumour risk was included in Zolgensma's prescribing information.

Patient advocates have pressed for more openness. SMA Europe, a patient advocacy organisation, had urged Novartis to explain what is known, what is uncertain, and what the findings could mean for treated children, after advocates complained the company was slow to share information.

Why It Matters

For the more than 6,000 children who have received Zolgensma, and for families of children now being considered for it or for Itvisma, the announcement changes the conversation around a treatment many regarded as a one-time cure. The therapy remains a remarkable advance for a disease that was once a death sentence in infancy, but parents and doctors must now weigh a confirmed, if rare, cancer risk that was previously described as theoretical.

The findings also reach beyond one drug. Gene therapies built on AAV vectors are used or in development for dozens of conditions, and the assumption that these vectors rarely integrate into the genome has been central to their safety case. Confirmed integration events in Zolgensma, FBX-101 and RGX-111 will force a harder look at long-term follow-up.

See also: the FDA salmonella alert for Darwin's cat food and the Marathon Health breach affecting 5.7 million people.

What Happens Next

The FDA said it is evaluating whether regulatory action is appropriate and whether the current prescribing information and long-term follow-up studies are adequate. That could lead to a strengthened warning on the label or new monitoring requirements, although the agency has not said what form any action would take.

Novartis is conducting long-term follow-up safety studies, and the FDA said patients receiving either product should be monitored for tumour formation. Doctors who see a tumour in a treated patient should contact Novartis Gene Therapies at 1-833-828-3947, or report it to the FDA through MedWatch at 1-800-FDA-1088.

Frequently Asked Questions

What is Zolgensma?
Zolgensma is a one-time gene therapy for spinal muscular atrophy in children under two. It uses a modified virus, an AAV vector, to deliver a working copy of the SMN1 gene in one intravenous infusion. It was first approved in the United States in May 2019.

How many children have developed tumours after Zolgensma?
Novartis has received nine tumour reports since 2019. Three involved the GLI1 oncogene; in two, analysis confirmed the therapy's vector DNA had integrated into the patients' DNA.

Does the risk affect Itvisma?
Yes, according to the FDA, because Itvisma uses the same vector and construct. It is injected into the spinal fluid for patients aged two and older, and no tumour cases have been reported after it to date.

Should parents of treated children be worried?
The FDA says the benefits continue to outweigh the risks, and families should not stop or change treatment without speaking to their child's doctor.

What should doctors do if a tumour develops?
Contact Novartis Gene Therapies at 1-833-828-3947 or report the case to the FDA through MedWatch at 1-800-FDA-1088.