A phase II clinical trial of chidamide in combination with toripalimab in patients with advanced soft tissue sarcoma

11566 Background: Chidamide is an oral subtype-selective histone deacetylase inhibitor which is effective on the patients with hematological tumors and reported to enhance the efficacy of checkpoint blockade therapies and regulate the host immune response. Here, we report preliminary results of Chidamide in combination with Toripalimab in soft tissue sarcoma (STS) patients. Methods: An open, single arm, phase II study of Chidamide with Toripalimab in patients with advanced soft tissue sarcoma after failure of standard treatment was conducted. Eligible patients could have any number of prior therapies, excluding HDAC inhibitors and immune checkpoint inhibitors treatment. All patients received Chidamide orally at 30mg twice weekly in combination with intravenous Toripalimab 240mg every 21 days until progression or unaccepted toxicity. The primary endpoint was RECIST1.1 objective response rate (ORR). The secondary endpoint included progression free survival (PFS), overall survival (OS), disease control rate(DCR) and safety. Results: Forty-six patients with advanced soft tissue sarcoma were enrolled. The median age of the patients was 47 years and the median prior lines of therapy were 3. The main subtypes included leiomyosarcoma (30.4%), well/dedifferentiated liposarcoma (30%), myxoid/round cell liposarcoma (7%), undifferentiated sarcoma(9%), and osteosarcoma (7%). Treatment was well tolerated with the most common adverse events mainly in grade Ⅰ and grade Ⅱ, including thrombocytopenia (43.5%), nausea(28.3%), neutropenia(23.9%), fatigue (17.4%) and hypothyroidism(15.2%). Among 46 efficacy-evaluable patients, the overall response rate and disease control rate were 23.9% and 80.4%, respectively. The median time to an initial response was 3 months (range, 2 to 14), and the 3-mon and 6-mon progression-free survival rate were 92.7% and 58.9%, respectively. Conclusions: Chidamide with Toripalimab every 21 days was well tolerated and showed promising efficacy in patients with advanced STS. Clinical trial information: NCT04025931 .