SUN-926 Malignant Transformation of a Benign Glucagonoma After 13 Years

Abstract

Glucagonoma are rare neuroendocrine tumors arising solely in the pancreas and approximately 25 % of glucagonoma cases start in a benign form. We hereby report a 76 -year-old male who was initially diagnosed with asymptomatic benign glucagonoma. Follow-up surveillance 13 years later shows that the tumor has undergone differentiation into a malignant form. Case Report: A 63-year-old man was referred for evaluation of an enhancing lesion (2.7 cm) at the pancreatic tail. He was completely asymptomatic with normal physical exam. Initial labs: normal except for elevated serum glucagon level (206 pg/mL, ref 0–60). A 2-hour oral GTT confirmed the autonomy of glucagon secretion by the tumor. Somatostatin and other tumor markers were normal. PET scan showed abnormal uptake at the distal pancreatic tail, correlating with the CT scan findings. The patient underwent laparoscopic distal pancreatectomy, with removal of a 2.8cm mass which predominantly expressed glucagon. Plasma glucagon level in the peripheral venous blood and intraoperative splenic vein dropped to <50 pg/mL immediately after the surgical resection. Following surgery patient remained completely asymptomatic for the next 13 years with normal blood glucose, glucagon, insulin, chromogranin levels, complete blood count and liver functions. Additionally patient continued to have normal surveillance MRIs of the abdomen. 13 years following removal of pancreatic mass, an elevated glucagon serum level (230 pg/mL) was noted on routine surveillance screening. At this time patient also remained asymptomatic. Abdominal MRI and PET scan revealed a 4-cm pancreatic mass with hepatic metastases. Biopsy of the hepatic lesion confirmed glucagonoma. Patient was treated with Lanreotide which has normalized the serum glucagon levels and the tumor size remained stable for the 12 months of follow up. Discussion: In our patient the glucagon secreting tumor without any classic presenting symptoms was found incidentally and the asymptomatic glucagonoma treated surgically presumably at an earlier stage. It is known that some glucagonomas are associated with serum levels of the peptide in the “physiologically elevated” range, even in the presence of necrolytic migratory erythema. The complete remission without any treatment lasting for more than 13 years confirmed the benign nature of the tumor. It is also reported that gluconomas less than 2 cm in size has less potential for metastasis. The usual recommendation is to monitor these patients post-resection to a maximum of 10 years although in our patient the malignant nature of the tumor was expressed 13 years after initial resection. The reason for malignant transformation after this prolonged period remains unknown. This case highlights the importance of continuous monitoring neuroendocrine tumors even beyond 10 years after surgery.