I completely forgot to update this, got the results earlier this week. Apparently, the cause of death was renal failure (chronic?) and there were signs of dehydration, hyperuricemia and septicemia. No mentions of any cysts/tumors or specific sources of the septicemia.
At least the crypto test came back negative.
I'm trying to read up on the subject right now, unfortunately I don't know how much of what applies to humans also applies to reptiles. Most sources seem to focus on dietary issues.