AKT-2500

A 65-year-old man presents to the General Practice Surgery with jaundice.
On examination, he has an enlarged, nodular liver. He is referred to hospital where a computed tomography (CT) scan of his abdomen reveals a cirrhotic liver with a large mass. A CT-guided biopsy of the mass demonstrates a malignant tumour derived from hepatic parenchymal cells.
What is the most likely causative agent in this patient?