(P 373) COMPLETE RESPONSE TO FRONT-LINE PEXIDARTINIB IN SYMPTOMATIC TEMPOROMANDIBULAR JOINT TENOSYNOVIAL GIANT CELL TUMOR

Objective: Tenosynovial giant cell tumor (TGCT) diffuse type is a rare (1.8-8 cases/million/year), locally destructive lesion arising from the synovium, with proliferation often driven by overproduction of colony-stimulating factor 1 receptor (CSF-1R). Surgical resection is standard of care, with high recurrence rates (60-70%) and often significant morbidity. Pexidartinib, a small molecule CSF-1R inhibitor, results in excellent overall response rates (>60%) and is increasingly utilized in the front-line to minimize surgical morbidity.
Here we present a unique case in TGCT management, a 51 year old male patient who presented with 2 years of right temporomandibular joint (TMJ) pain and a 2.6cm expansile TMJ lesion on imaging. Biopsy was consistent with TGCT, and multidisciplinary case review determined surgical resection would require extensive reconstruction with the potential for reduced joint function, nerve injury, and persistent post-operative pain. Given critical location, pexidartinib was initiated as an alternative first line treatment modality.

Methods: Data collected retrospectively by manual chart review, including time to response (TTR) and patient reported outcomes such as symptomatic benefit and adverse effects (AEs). Patient received standard dose of 250mg pexidartinib twice daily and was monitored as per the TURALIO-REMs program requirements.

Results: The patient’s pain improved within 1 month of pexidartinib initiation. TTR by RECIST was 5.8 months, including resolution of extension into critical surrounding structures. Complete response was noted by 17.8 months, with resolution of all associated symptoms. AEs included grade 1 fatigue and hair depigmentation; no grade 3-4 AEs observed. Given excellent response, pexidartinib was discontinued at 18.5 months. At time of submission, duration of response measured 20 months.

Conclusion: Here we present a unique case of TGCT of the TMJ where surgery would have meant catastrophic morbidity. Pexidartinib therapy represents a feasible, well-tolerated front-line management strategy in cases where surgical morbidity is high, offering symptom relief and the opportunity for tumor resolution.