Vorasidenib for Certain IDH-Mutant Gliomas: Is It Worth It?

The emergence of vorasidenib, the first targeted therapy for certain gliomas with IDH mutations, has ignited a wave of excitement in both patient and physician spaces.

After years with limited treatment options, experts hailed vorasidenib “a promising breakthrough,” “a paradigm shift,” a “new hope,” and “probably the most important advance in the treatment of low-grade gliomas in the last decade.”

Promising results from vorasidenib’s pivotal INDIGO trial fueled petitions and patient advocacy circles to push for the drug’s approval. And, in August 2024, the US Food and Drug Administration (FDA) approved vorasidenib for grade-2 astrocytomas or oligodendrogliomas with an IDH1 or IDH2 mutation.

But following the approval, some experts expressed concerns and doubts about the drug and the INDIGO trial, bringing a host of unanswered questions into sharper focus.

In an editorial entitled “Vorasidenib: A new hope or a false promise for patients with low-grade glioma?” Stanislav Lazarev, MD, and Kunal K. Sindhu, MD, both radiation oncologists from Icahn School of Medicine at Mount Sinai, New York City, suggest that the FDA approval “might be premature given the high cost of this drug and lack of clear benefit over standard treatments.”

Another recent critique also pointed to the lack of clear evidence that vorasidenib is superior to the prevailing standard of care, despite the drug’s high cost. These authors noted that “patients want to live longer, and if not, at least live better,” but “based on the INDIGO study, it is impossible to say whether vorasidenib can provide either.”

Vorasidenib is now one of the most expensive cancer therapies, with an annual cost of nearly $500,000 , but the INDIGO trial did not explore whether the drug led to improved overall survival or better quality of life. Among the trial’s design flaws, experts called out the use of progression-free survival as the primary outcome, instead of overall survival, and the use of an inappropriate comparator group.

INDIGO was a phase 3 trial that included 331 adult patients (median age, 40.5 years) with grade-2 IDH-mutant recurrent or residual glioma after surgery. To be eligible, patients had to be followed for at least 1 year, and up to 5 years, post-surgery and had to be considered appropriate candidates for a watch-and-wait approach.

Participants were randomly assigned to receive either 40 mg of vorasidenib or a matching placebo orally, once daily, in continuous 28-day cycles until imaging-confirmed tumor disease progression or unacceptable toxicity, at which point crossover to vorasidenib from placebo was permitted. Over one third (n = 58) of patients in the placebo group crossed over and 90% of them (n = 52) received vorasidenib.

Median progression-free survival was significantly better in the vorasidenib group at 27.7 months vs 11.1 months in the placebo group (hazard ratio [HR], 0.39).

A key secondary endpoint — time to next intervention — was also significant; the likelihood of being alive and not receiving further treatment at 18 months was 85.6% in the vorasidenib group and 47.4% in the placebo group (HR, 0.26). This finding indicates that most patients receiving vorasidenib could delay chemoradiation for 18 months or longer.

Despite these impressive outcomes, some experts noted that using progression-free survival as the primary endpoint was a major flaw of the INDIGO trial because, currently, there is no evidence that progression-free survival is a reliable surrogate endpoint for overall survival in this setting.

The high rate of crossover to vorasidenib is another issue because it may limit a longer-term analysis of overall survival. If, for instance, overall survival is the same between the groups, it could signal that the drug is effective in both groups or, alternatively, that the drug has no effect on survival in either group.

“That is a legitimate concern,” Seema Nagpal, MD, a neuro-oncologist at Stanford University in Palo Alto, California, and a site principal investigator for the INDIGO trial, said in an interview with Medscape Medical News. “We don’t know that this drug changes overall survival, and I think we’re not going to get a super clean answer on that.”

Another major issue centers on the standard of care assigned to control patients in the INDIGO trial.

In the trial, vorasidenib was compared with placebo — an appropriate standard-of-care comparison for patients with low-risk gliomas. These patients often initially undergo watch-and-wait to delay chemoradiation. But Lazarev and Sindhu argue that the patients in INDIGO were really high risk, which means the control group should have received the standard of care for these patients: Chemoradiation following surgery.

This question about the appropriate standard of care stems from ongoing uncertainty about the distinction between high- and low-risk gliomas.

The classification for gliomas falls into either low risk or high risk for early disease progression. The RTOG 9802 criteria, often used for glioma risk stratification, defines low-risk patients as those younger than 40 years with gross total resection and high-risk patients as those aged 40 years or older with any extent of resection or those younger than 40 years with subtotal or biopsy resection.

But an evolving understanding of genetic anomalies that affect prognoses in this tumor type has muddied the current high- and low-risk distinctions.

“People haven’t totally figured out what high and low risk means,” Nagpal acknowledged.

This uncertainty has spilled over into the INDIGO trial.

While the trial excluded patients who had any features indicating high risk, such as brain stem involvement or neurocognitive deficits, the researchers also did not explicitly define patients as low risk. However, the inclusion criteria specified that patients had to be observed for at least 1 year after surgery and be considered appropriate for a watch-and-wait protocol, which does suggest patients were considered low risk, said Nagpal.

Still, some experts argue that the patients in INDIGO were not low risk.

Patients had residual or recurrent disease so “wouldn’t be classified as low risk,” said Sindhu in an interview with Medscape Medical News. The standard of care for these patients is chemoradiation, Lazarev added.

“The definition of a phase 3 clinical trial is that you compare the novel intervention to the standard of care,” said Lazarev. “Level 1 evidence clearly shows that omitting chemoradiation leads to worse outcomes, with patients literally dying sooner. For the investigators to knowingly exclude this proven treatment raises serious ethical and methodological questions about the study’s design.” 

In a recent opinion piece, Nagpal agreed that most patients selected for INDIGO would not have been considered low risk by many providers. All patients selected for INDIGO had postoperative residual/recurrent disease and many were older than 40 years.

But, Nagpal explained, the risk stratification of the INDIGO patients was still lower than what is commonly considered high risk. The patients had all been observed for a year or more already, “so by definition, the clinician treating them already decided they were not high risk,” she said.

In another recent opinion piece, oncologists suggested that because patients in the INDIGO trial do not squarely fall into either category, instead representing a “grey area,” it’s time to create a new risk category.

“Perhaps the time has come to abandon the old binary risk stratification (“low risk” vs “high risk”), which still contains arbitrary elements (such as the age cutoff), proving impractical in real-world clinical decision-making, and to adopt a new one, also taking into account many emerging prognostic biomarkers,” the authors wrote.

Despite the uncertainty surrounding risk categories, the INDIGO authors justified their study design.

A watch-and-wait period for patients in the trial, which “represents the earliest clinical phase in tumorigenesis of IDH-mutant WHO grade-2 glioma,” is “an opportunity to detect a clear signal of antitumor activity for new therapies in placebo-controlled trials” and “postpone the use of radiation therapy and chemotherapy,” the authors explained.

Lazarev, however, questioned the premise that chemoradiation should be delayed.

Oncologists’ desire to delay chemoradiation for their patients reflects “a limited understanding of modern irradiation therapy,” Lazarev said. “Modern technology has improved dramatically. We’re more precise, our understanding about late side effects is better. So, the big picture is that the absolute risk of late neurocognitive affects that actually will affect patients’ quality of life, their ability to work, go to school, succeed on a personal or professional level is exceedingly low.”

Nagpal strongly disagreed.

“Please come to my clinic and ask an actual patient,” said Nagpal. “Once a radiation oncologist has irradiated the patient, they almost never seen them again. People who are on the medical side, who follow these patients from beginning to end, recognize that delaying radiation is a huge deal.”

Although vorasidenib isn’t a cure, Nagpal said, it is a less toxic way to delay radiation 
“because that is a real and disabling thing” for patients and is why neuro-oncologists are excited about alternative treatment options.

Another issue surrounding the vorasidenib approval lies in the FDA’s vague prescribing information. The prescribing information does not specify that patients should be followed for at least 1 year post-surgery or that patients need to be lower risk. Prescribing physicians may, therefore, think vorasidenib is appropriate for any patient with a grade-2 IDH mutant glioma at any time and defer or not offer chemoradiation to high-risk patients.

Amid lingering questions about the INDIGO trial design and ongoing uncertainties about how to define and treat this patient population, experts remain divided on whether vorasidenib is worth it.

“If vorasidenib is truly transformative, it should be feasible to demonstrate its superiority over chemoradiotherapy,” Lazarev and Sindhu wrote. “For a drug with such a staggering price tag, an imperative should be placed on the investigators and manufacturer to provide clear evidence of efficacy, whether in terms of improved [overall survival] or quality of life, before vorasidenib is recommended for the treatment of IDH-mutant low-grade gliomas.”

The INDIGO trial was supported by Servier, the manufacturer of vorasidenib. Many of the study authors reported employment or support from the company. Nagpal reported consulting fees from Servier and AnHeart Therapeutics. Lazarev and Sindhu reported no relevant financial relationships.