Pexidartinib significantly improved overall response rates and functioning in patients with advanced tenosynovial giant cell tumors (TGCT), based on the final results of the ENLIVEN study, presented at the annual meeting of the American Society of Clinical Oncology in Chicago.

“Pexidartinib, a novel CSF1 receptor inhibitor, may offer a relevant treatment option for patients with TGCT, which is associated with severe morbidity or functional limitations, and for which surgery is not recommended,” said William Tap, MD, of Memorial Sloan Kettering Cancer Center, New York.

Compared with placebo in patients with advanced, symptomatic TGCT, pexidartinib significantly improved overall response rates; RECIST was 39% with pexidartinib and 0% with placebo. Tumor volume score improvement was 56% with pexidartinib and 0% with placebo. Both results were significant at P less than 0.0001.

“Importantly, these responses correlated with improved patient symptoms and function,” Dr. Tap said. “Pexidartinib was generally well tolerated with serious, nonfatal liver toxicity with increased bilirubin in 4% of patients.” The majority of other adverse events with pexidartinib (hair color changes, vomiting, fatigue, dysgeusia, and periorbital edema) were less than grade 3.

The primary treatment for these patients is surgery; there are currently no approved systemic therapies for advanced tenosynovial giant cell tumor. In previous studies by others, imatinib, evaluated in 27 patients, was associated with a 19% overall response rate (ORR). Nilotinib, evaluated in 51 patients, was associated with a 0% ORR at week 12.

ENLIVEN is a double-blind, randomized, placebo-controlled international, phase 3 study whose participants had histologically confirmed, advanced, symptomatic TGCT of greater than 2 cm. Several had previous surgeries, but further surgical resection would have been associated with the potential for worsening functional limitations or severe morbidity.

In ENLIVEN, 61 patients were randomized to pexidartinib and 59 to placebo. All had recurrent or inoperable TGCT. Patients received placebo or pexidartinib 1000 mg/day (split, BID for 2 weeks) then 800 mg/day (split BID for 22 weeks).

Nine patients in the active treatment group and 11 in the placebo group discontinued therapy. Eight patients discontinued pexidartinib due to hepatic adverse events; all serious hepatic events appeared in the first 2 months of treatment.

At 25 weeks, blinded reviews of MRI scans were performed. A partial response was seen in 12 (52%) patients and stable disease was seen in 7 (30%), based on RECIST 1.1.

Also at week 25, pexidartinib-treated patients did better on scores of functional endpoints related to range of motion, PROMIS physical function, stiffness, and BPI worst pain response. Based on functional endpoints, 9 of 61 (15%) had a complete response and 15 (25%) had a partial response, for an overall response rate of 24 (39%); P less than 0.0001.

None of the 59 patients in the placebo group had a response.

Tumor volume scores at week 25 were complete in 3 (5%) and partial in 31 (51%); overall response rate was 34 (56%); P less than 0.0001. Disease was stable in 14 (23%), progressive in 1 (2%), and not evaluable in 12 (20%). There were no complete or partial responses in the placebo group; disease was stable in 45 (76%), progressive in 2 (3%), and not evaluable in 12 (20%).

Dr. Tap disclosed consulting or advisory roles with Daiichi Sankyo, the maker of pexidartinib; as well as Adaptimmune; Blueprint Medicines; Eisai; EMD Serono; Immune Design; Janssen; Lilly; Loxo; Novartis; Plexxikon; TRACON Pharma. Clinical trial information: NCT02371369.

SOURCE: Tap W et al. ASCO 2018 (annual meeting of the American Society of Clinical Oncology), Abstract 11502.

ENLIVEN: Pexidartinib improves symptoms, function in patients with advanced tenosynovial giant cell tumors