You are answering a USMLE-style medical question. Question: A 55-year-old man with chronic hepatitis B virus infection comes to the physician because of generalized fatigue and a 5.4 kg (12 lb) weight loss over the past 4 months. Physical examination shows hepatomegaly. Laboratory studies show an α-fetoprotein concentration of 380 ng/ml (N < 10 ng/mL). A CT scan of the abdomen with contrast shows a solitary mass in the left lobe of the liver that enhances in the arterial phase. Which of the following is the most likely underlying pathogenesis of this patient's current condition? Options: A) Overexpression of secretory hepatitis antigen B) Intracellular accumulation of misfolded protein C) Gain of function mutation of a proto-oncogene D) Integration of foreign DNA into host genome " Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.