The Oncologic Drugs Advisory Committee (ODAC) of the Food and Drug Administration voted to support approval of the small molecule kinase inhibitor pexidartinib for the treatment of adults with symptomatic tenosynovial giant cell tumor (TGCT) associated with severe morbidity or functional limitations and is not amenable to improvement with surgery.
The drug was favored by a 12-3 margin (no abstentions), with the majority of panel members agreeing that it offers clinical benefits that outweigh significant risk for elevated liver enzymes and small but real potential for serious or even fatal liver injury.
The FDA usually follows the recommendation of advisory committees in deciding final approval. Daiichi Sankyo plans to market the drug under the trade name Turalio.
Final approval and marketing of the drug will hinge on a mandatory Risk Evaluation and Mitigation Strategy that will require certification of prescribers, patient participation in education about the need for frequent liver function testing and the signs and symptoms of liver injury, and distribution of the drug only to certified pharmacies.
Both the ODAC panel members and pexidartinib’s manufacturer, Daiichi Sankyo, agreed that the drug is effective, but opinions about the degree of clinical benefit and the risk-benefit ratio differed.
TGCT is a rare, nonmalignant, and nonlethal tumor of the synovium, bursae, or tendon sheath that can be locally aggressive, and for some patients completely disabling. Surgery is the primary mode of treatment, but less than 10% of patients have disease that is not amenable to resection; for these patients treatment options are limited, because there are no approved systemic therapies for the disease.
Evidence submitted to support the application comes from the phase 3 ENLIVEN trial, in which patients with TGCT not amenable to surgery were randomly assigned to receive pexidartinib or placebo. The trial was designed to enroll 126 patients to provide 90% power to detect a difference in objective response rate at a two-sided alpha level of 0.05, assuming an overall response rate of 10% with placebo, and 35% with pexidartinib.
The actual trial enrollment, however, fell a little short, with a total of 120 patients randomized.
The ORR at week 25 as assessed by blinded independent central reviewers, the primary endpoint, was 39% for the 61 patients in the pexidartinib group, compared with 0% for the 59 patients in the placebo group (P less than .0001).
There were also statistically significant improvements in the pexidartinib arm at week 25 in the secondary endpoints of mean change in range of motion (ROM), ORR by tumor-volume score at week 25, mean change from baseline in the Patient-Reported Outcomes Measurement Information physical function scale, and mean change in the Worst Stiffness numeric rating scale item. There were no significant differences between the groups for worst pain, however.
The FDA briefing document notes that “interpretation of the results of the secondary endpoints should be viewed with caution as there was a high proportion of missing data at week 25 for ROM, physical function, and worst stiffness (27%, 43% 43%, respectively); the proportion of patients with missing data was similar across study arms.”