FDA Investigates Cancer Risk with Zolgensma Gene Therapy

The U.S. Food and Drug Administration (FDA) is investigating a serious potential cancer risk associated with Zolgensma (onasemnogene abeparvovec), a gene therapy used to treat spinal muscular atrophy (SMA). The investigation follows postmarketing reports of tumors in patients treated with Zolgensma, including confirmed cases in which genetic material from the therapy became integrated into a patient’s genome in a manner associated with cancer development.

The findings raise important questions about the long-term safety of adeno-associated virus (AAV) vector-based gene therapies, particularly the potential for unintended genetic changes that may contribute to tumor formation.

How Can Gene Therapy Contribute to Cancer?

Zolgensma uses a modified AAV vector to deliver a functional copy of the SMN1 gene, which is defective or missing in patients with SMA. AAV-based gene therapies are generally designed to deliver genetic material without permanently integrating it into the patient’s chromosomes. However, integration can occasionally occur.

When introduced genetic material integrates near a gene that regulates cell growth, it may alter that gene’s activity and potentially contribute to cancer development. This process is known as insertional oncogenesis.

FDA reports three cases involving tumors associated with the GLI1 oncogene, a gene capable of promoting cancer when abnormally activated. In two cases, molecular analysis confirmed that DNA from the Zolgensma vector had integrated into the patient’s genome, placing a regulatory sequence from the therapeutic construct upstream of or within GLI1. The mechanism responsible for GLI1 overexpression in the third case remains under investigation.

These findings are particularly significant because they provide molecular evidence connecting gene therapy vector integration with tumor development, rather than identifying only a statistical association between treatment and cancer.

FDA Identifies Potential Risk Across Two SMA Gene Therapies

FDA has determined that the potential risk applies to both Zolgensma and Itvisma, another SMA gene therapy containing the same AAV vector and genetic construct. The products differ in their approved populations and routes of administration:

• Zolgensma: Administered intravenously to children younger than 2 years.
• Itvisma: Administered intrathecally to adults and children aged 2 years and older.

FDA reports that no cases of neoplasia have been reported following Itvisma administration to date. However, because the two products contain the same vector and construct, FDA considers the identified risk relevant to both therapies.

The agency is also monitoring other AAV-based gene therapy programs for similar safety concerns.

A Previously Theoretical Risk Becomes a Documented Concern

The prescribing information for both Zolgensma and Itvisma already warns of a theoretical risk of tumor formation associated with AAV vector DNA integration. The new postmarketing findings represent an important development in understanding that risk.

FDA is evaluating whether the existing prescribing information adequately communicates the potential danger and whether current long-term follow-up studies are sufficient to identify and monitor affected patients. Novartis, the manufacturer, is conducting long-term safety follow-up studies.

FDA has also identified published reports of AAV vector integration-associated oncogenesis involving other investigational gene therapy programs, suggesting that the concern may extend beyond a single product.

FDA Continues to Support Approved Uses

Despite the seriousness of the findings, FDA states that the overall benefits of Zolgensma and Itvisma continue to outweigh their potential risks for their approved uses. The agency has not announced a withdrawal of either product.

Instead, FDA is investigating the reported malignancies, evaluating the adequacy of existing safety warnings and follow-up requirements, and considering whether additional regulatory action is warranted.

Patients and clinical trial participants who receive these therapies should be monitored for tumor formation. Healthcare providers can report suspected adverse reactions to FDA through its MedWatch program.

MDP Perspective: Long-Term Safety Is Essential to Gene Therapy Development

The FDA investigation illustrates a fundamental challenge in gene therapy development: the potential for delayed adverse effects that may not become apparent during the relatively short observation periods of premarket clinical trials.

Gene therapies can provide substantial benefits, particularly for patients with serious genetic disorders and limited treatment options. However, the introduction of genetic material into human cells creates safety considerations that differ from those associated with many conventional pharmaceuticals.

Although AAV vectors are generally considered to have a low propensity for genomic integration, the reported cases demonstrate that integration events can have serious consequences when they affect genes involved in cell growth and regulation.

For gene therapy developers, these findings reinforce the importance of evaluating vector integration, genomic safety, long-term patient monitoring, and postmarketing adverse-event surveillance. They also demonstrate why FDA’s oversight of advanced therapies extends well beyond initial product approval.

The agency’s continuing investigation will be important in determining whether additional warnings, monitoring requirements, or other regulatory measures are necessary. For now, FDA’s position remains clear: the benefits of these therapies continue to outweigh their identified risks, but the emerging evidence warrants careful investigation and continued long-term surveillance.