A 58-year-old woman presents with 9 months of pruritus and 1 month of jaundice noticed by others. No abdominal pain, normal appetite and bowel movements. Physical exam shows marked jaundice, excoriations, liver 3 cm below the costal margin (firm consistency), spleen 6 cm below the costal margin. Labs: TBil 85.5 μmol/L, CB 46.8 μmol/L, albumin 30 g/L, globulin 42 g/L, ALT 56 U/L, ALP 820 U/L, GGT 94.5 U/L, IgG 19.6 g/L, IgA 16.9 g/L, IgM 8.6 g/L. Ultrasound shows hepatosplenomegaly, common bile duct 6 mm, no intrahepatic bile duct dilation. The most likely diagnosis is: