Safety and preliminary efficacy of pembrolizumab following trans-arterial chemoembolization for hepatocellular carcinoma: the PETAL phase Ib study.

TACE may prime adaptive immunity and enhance immunotherapy efficacy. PETAL evaluated safety, preliminary activity of TACE plus pembrolizumab and explored mechanisms of efficacy. Patients with liver-confined HCC were planned to receive up to 2 rounds of TACE followed by pembrolizumab 200 mg every 21 days commencing 30-days post-TACE until disease progression or unacceptable toxicity for up to 1 year. Primary endpoint was safety, 21-days dose-limiting toxicities (DLT) from pembrolizumab initiation. Secondary endpoints included progression-free survival (PFS) and evaluation of tumour and host determinants of response. Fifteen patients were included in the safety and efficacy population: 73% had non-viral cirrhosis, median age was 72 years. Child-Pugh (CP) class was A in 14 patients. Median tumour size was 4 cm. Ten patients (67%) received pembrolizumab after 1 TACE, 5 patients after 2 (33%). Pembrolizumab yielded no synergistic toxicity nor DLTs post-TACE. Treatment-related adverse events occurred in 93% of patients most commonly skin rash (40%), fatigue and diarrhoea (27%). After a median follow-up of 38.5 months, objective response rate (ORR) 12 weeks post-TACE was 53%. PFS rate at 12 weeks was 93% and median PFS was 8.95 months (95%CI 7.30-NA). Median duration of response was 7.3 months (95%CI: 6.3-8.3). Median OS was 33.5 months (95%CI: 11.6-NA). Dynamic changes in peripheral T-cell subsets, circulating tumour DNA, serum metabolites and in stool bacterial profiles highlight potential mechanisms of action of multi-modal therapy. TACE plus pembrolizumab was tolerable with no evidence of synergistic toxicity, encouraging further clinical development of immunotherapy alongside TACE.