Patients who undergo transplants are typically put on immunosuppressant medication to help their bodies accept the new liver. However, suppressing the immune system can allow cancer cells to grow more quickly, said Alexander.
Warshaw said patients who get immunosuppressants can respond very differently to regular cancer treatments.
"All bets are off" for understanding what type of treatment will be successful, Warshaw said.
Still, it is not clear why Jobs is taking this leave, his third since 2004. Aside from tumor recurrence, he could also be dealing with organ rejection or a possible hormone imbalance if the tumor is active.
In general, Metz said neuroendocrine pancreatic tumors are a relief "because patients stick around for a long time and we can use various modalities to treat them. The downside is that the likelihood of 'curing' people once they've metastasized is very low."