
I was under the impression that an accurate diagnosis of liver disease could only be from a biopsy of the liver. Blood tests can show an indication but are not definitive.
Has your vet suggested a special diet at all or done any other tests, not just blood tests?
I lost my old boy to liver disease/failure last month and his decline was rapid. He'd had various blood tests, urine tests, bile acid concentration tests etc about 6 months previously and all came back within the normal range. He showed few symptoms and was basically a happy, but obviously older dog (he was nearly 13). He had had regular tests anyway because he was on long-term pain relief for his arthritis and nothing extraordinary showed up. Within the space of 5 days he went downhill and was pts (he had a biopsy and the result came back that the liver was full of scar tissue).
I'd also be questioning the diagnosis, although the symptoms you describe could point towards liver disease. With regard to the skin tumours I think you need to discuss with your vet really.
Good luck! :)