Background: Tremelimumab is a fully human monoclonal antibody that binds to CTLA-4 expressed on the surface of activated T lymphocytes and results in inhibition of B7-CTLA-4-mediated downregulation of T-cell activation. Transcatheter arterial chemoembolization (TACE), radiofrequency ablation (RFA) and cryoablation (CA) have been shown to induce a peripheral immune response which may enhance the effect of anti-CTLA4 treatment in patients with advanced HCC. Methods: Patients with HCC [Childs Pugh A/B7; BCLC B/C; ECOG 0/1; post-sorafenib (BCLC stage C only)] or refractory BTC were enrolled in a study of Tremelimumab combined with subtotal TACE, RFA or CA performed on week 6. All BTC patients received RFA as the immune-stimulant in combination with tremelimumab. Tumor biopsies were performed at baseline and at time of RF/TACE. Results: 34 pts enrolled (28 HCC, 6 BTC). Characteristics: M:F 26:8; Median age 54(range 42-76); In HCC pts cirrhosis present in 17pts, BCLC Stage B/C: 9/19; Hepatitis B/C/neg: 4/15/9. 13 pts received TACE, 16 underwent RFA (inc 6 BTC pts), 3 CA during week 6 of tremelimumab therapy. 2 pts did not receive an ablative procedure. No DLT encountered. Most common toxicity was pruritus. One patient developed pulmonitis and was taken off study but remained disease-free at 16m. Of N = 17 pts evaluable for response outside of TACE/RFA-treated lesion 4 (23.5%) achieved confirmed partial responses. 8 of 9 pts with quantifiable HCV experienced a marked reduction in viral load. 6-week tumor biopsies showed immune cell infiltration on all evaluable patients. Median PFS for the evaluable HCC population (N = 25) was 5.7m. Conclusions: Tremelimumab in combination with subtotal TACE, RFA or CA in patients with advanced HCC and BTC is safe and feasible. Obtaining tumor biopsies at baseline and at the time of RFA/TACE is safe. Evidence of immune cell infiltration was seen on evaluable patients. Encouraging clinical activity seen with objective confirmed responses, PFS 5.7m and possibly surrogate reductions in HCV viral load. Clinical trial information: NCT01853618