Clinical benefit of imatinib in patients with relapsed tenosynovial giant cell tumor/ pigmented villonodular synovitis (TGCT/PVNS).

e23561 Background: TGCT/PVNS is an uncommon benign but locally aggressive tumor that affects joints and can lead to significant morbidity. It is characterized in most cases by a t(1;2) translocation that leads to overexpression of colony-stimulating factor 1 (CSF-1) and the accumulation of inflammatory cells that express CSF-1 receptor (CSF-1R) in the affected joints. Imatinib inhibits the tyrosine kinase activity of CSF-1R. Methods: We retrospectively reviewed patients with TGCT/PVNS who received treatment with imatinib within Kaiser Permanente Northern California. Results: Nine patients with relapsed TGCT/PVNS were treated with imatinib from 2019 to 2022. Median age was 43 years. 6 patients were female. The imatinib dose was 400 mg daily. All patients had been treated with surgery previously and relapsed, and further surgery was considered not to be beneficial. All patients presented with persistent joint pain that affected joint mobility and walking. After imatinib therapy was initiated, 7 patients (78%) reported significant improvement in their symptoms, while 2 patients (22%) reported no significant changes. Improvement in symptoms occurred soon after starting therapy, ranging from 3 days to 5 weeks. 8 patients (89%) had stable disease by RECIST criteria based on MRI, and 1 patient was not evaluable. 5 patients are still receiving imatinib currently. The longest treatment duration is 27 months. 4 patients required a dose reduction secondary to toxicity, and 3 patients discontinued therapy (2 patients with G3/4 hepatotoxicity and 1 patient self-discontinued treatment). 2 patients who discontinued imatinib continue to experience resolution of joint pain and other symptoms 10 and 24 months later respectively. Conclusions: Our study shows that treatment with imatinib can result in rapid and lasting symptomatic improvement in patients with relapsed TGCT/PVNS, even after treatment discontinuation. This suggests that imatinib can be an effective and safe treatment option for patients with relapsed TGCT/PVNS refractory or not amenable to further surgery.