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A phase Ib study of pembrolizumab following trans-arterial chemoembolization (TACE) in hepatocellular carcinoma (HCC): PETAL

e16195 Background: Trans-arterial chemoembolization (TACE) is the gold-standard for intermediate stage HCC. We hypothesised the ischemic and cytotoxic effect of TACE to boost anti-cancer immunity and to synergise with the anti PD-1 pembrolizumab (pembro). We designed a phase Ib study to test the safety and preliminary efficacy of pembro after TACE in intermediate HCC. Methods: PETAL study will enroll up to 32 patients with intermediate HCC to receive pembro 200 mg every 3 weeks for up to 1 year or until disease progression or unacceptable toxicity. The first safety-run-in phase includes 6 patients: if no dose limiting toxicities (DLTs) emerge over a 21-day window after first pembro, the others are enrolled in the expansion phase. Pembro is given within 30 days after 1 or 2 TACEs. The first phase includes 1 patient scoring Child-Pugh (CP)-B7 and the remaining have to be CP-A. Safety is the primary endpoint and is measured as the incidence of treatment-related adverse events (TRAEs), graded according to NCI CTCAEv4. Efficacy is the secondary endpoint and is evaluated as progression free survival (PFS) from first TACE, according to mRECIST criteria. Survival is estimated using Kaplan-Meier method. All the patients who have received at least one dose of pembro are evaluable for safety. Results: At the time of data cut-off, on the 14th of January 2022, 14 patients had received at least one dose of pembro. The median age was 72 (IQR: 63.3-74.6), 79% were male, 71% were cirrhotic, 29% had viral hepatis and 43% ECOG PS 1. One patient had Child-Pugh (CP) class B7 and 13 had A. The median number of nodules was 1.5 (IQR:1-2.8), and 4.1 cm (IQR: 3.7-4.5) the median diameter. Overall, 5 patients received 2 TACEs and 9 had 1. Patients received a median of 4.5 cycles (IQR: 2.3-6.5) of pembro. No DLTs emerged in the first phase. Treatment-related adverse events (TRAE) of any grade (G) were reported in 86% of participants, 21% of participants experienced G3 TRAEs, and there were no G4 or G5 TRAEs. Specific skin-related toxicity was the most frequently reported (35%) TRAE. No patients had treatment-related liver toxicity. Causes of treatment discontinuation were PD (n=7), TRAEs (n=1), clinical deterioration in the CP B patient (n=1), COVID pandemic (n=2) and withdrawal of consent (n=1); at the time of data cut-off, mPFS from first TACE was 10.8 months (95%CI: 6.63-14.97). Conclusions: Adjuvant pembro following TACE is manageable and tolerable with signs of activity. These results prompt the investigation in larger trials. Clinical trial information: NCT03397654. [Table: see text]