The median progression-free survival was 13.6 months for patients with nonenhancing tumors and 1.4 months for patients with enhancing tumors in a study of 66 adults with mIDH1 advanced glioma.
“On the basis of these data, additional clinical development of mIDH inhibitors for mIDH low-grade gliomas is warranted,” Ingo Mellinghoff, MD, of Memorial Sloan Kettering Cancer Center in New York, and colleagues wrote in the Journal of Clinical Oncology.
“This is not a home run but is of interest to the community,” said Lawrence Recht, MD, of Stanford (Calif.) University, who was not involved in this study. “Other companies are also developing agents like this.”
Considering that the ivosidenib study “is uncontrolled, one cannot say for sure that this wasn’t just the natural history of the disease,” Dr. Recht continued. “This type of tumor can behave very indolently, and patients can survive years without treatment, so this is rather a short interval to make a long-time statement. I think the authors are a bit overenthusiastic.”
The authors tested ivosidenib in 66 adults with mIDH1 glioma – 35 with nonenhancing glioma and 31 with enhancing glioma. Tumors had recurred after, or did not respond to, initial surgery, radiation, or chemotherapy.
The patients’ median age was 41 years (range, 21-71 years), and 25 patients (37.9%) were women. The most common tumor type at screening was oligodendroglioma in 23 patients (34.8%).
Patients received ivosidenib at doses ranging from 100 mg twice a day to 900 mg once a day. A total of 50 patients received the phase 2 recommended dose – 500 mg once a day. There were no dose-limiting toxicities, and there was no maximum-tolerated dose.
Adverse events of grade 3 or higher occurred in 19.7% of patients and included headache, seizure, hyperglycemia, neutropenia, and hypophosphatemia. Grade 3 or higher treatment-related adverse events occurred in two patients.
A total of 30 patients with nonenhancing tumors (85.7%) and 14 with enhancing tumors (45.2%) had a best response of stable disease. There was one partial response in a nonenhancing patient on 500 mg/day. The rest of the subjects had a best response of progressive disease.
The median treatment duration was 18.4 months among patients with nonenhancing tumors and 1.9 months among those with enhancing tumors. Discontinuation was caused byo progression in all but one case.
Among patients with measurable disease, tumor measurements decreased from baseline in 22 nonenhancing tumors (66.7%) and in 9 enhancing tumors (33.3%).
“Despite the heterogeneous patient population in our trial, the nonrandomized design, and the lack of central pathology review, the data from our trial suggest that ivosidenib has greater activity against nonenhancing gliomas than against enhancing gliomas,” the investigators wrote. “This finding may seem surprising because the absence of contrast enhancement is typically associated with impaired drug delivery.
“We hypothesize that ivosidenib may be more effective in nonenhancing gliomas because these tumors represent an earlier disease stage with fewer genetic alterations, reminiscent of the greater antitumor activity of the BCR-ABL inhibitor imatinib in earlier stages of chronic myeloid leukemia,” the investigators wrote.
The team also noted that the median progression-free survival for patients with nonenhancing gliomas in the current study “compares favorably to that reported for temozolomide” in advanced mIDH1 low-grade glioma, which was approximately 7 months.
This research was funded by Agios Pharmaceuticals, the company developing ivosidenib. Dr. Mellinghoff receives travel compensation from and is an adviser to the company. Several other investigators are employees. Dr. Recht disclosed no conflicts of interest.
SOURCE: Mellinghoff I et al. J Clin Oncol. 2020 Jun 12. doi: 10.1200/JCO.19.03327