Spontaneous Regression in Pancreatic Neuroendocrine Tumor.

Spontaneous regression (SR) of pancreatic neuroendocrine tumors (pNETs) is extremely rare. We herein report a 64-year-old man with a nonfunctioning pNET that was incidentally detected during an evaluation for back pain. Imaging showed a 30-mm mass in the pancreatic tail, but surgery was delayed because of an old myocardial infarction. Four months later, follow-up imaging revealed tumor shrinkage of 20 mm without treatment. Laparoscopic distal pancreatectomy confirmed a grade 3 pNET. While ischemia was considered, factors such as mild immune response or metabolic stress may have contributed. This case suggests that ischemia and other factors may also play a role. Further research is needed to elucidate the mechanisms underlying SR in neuroendocrine tumors.