Parathyrinoma (Ectopic Hypercalcemia Syndrome) is an islet cell tumor that causes signs and symptoms indistinguishable from those seen in parathyroid hyperplasia and adenoma.

The peptides secreted by parathyrinomas are structurally heterogeneous and differ immunologically from parathyroid hormones.

Thus they can not be measured by usual radioimmunoassay, which makes the diagnosis difficult.

Surgical removal of the islet cell tumour, or chemotherapy with streptozotocin in cases in which the tumour is not amenable to resection, causes a prompt lowering of blood calcium levels and the disappearance of symptoms.

Pancreatic islet cell tumors.Surgery. 1986 Jun;99(6):671-8.

Tumors arising from the pancreatic islet cells represent a heterogeneous group of lesions. Some tumors present with well-characterized syndromes, while others appear to be nonfunctioning. Eighty-four patients with pancreatic islet cell tumors operated on at the Cleveland Clinic during a 35-year period were reviewed. The tumor types include 21 nonfunctioning tumors, 41 insulinomas, 16 gastrinomas, two vasoactive intestinal polypeptide (VIP)-omas, two carcinoids, and two probable cases of pancreatic parathyrinoma. Eleven patients had multiple endocrine neoplasia type I syndrome. Preoperative localization was possible in 63% of patients in whom it was attempted. Complete mobilization of the head and distal pancreas with bimanual palpation of the entire gland is critical for intraoperative tumor localization. Distal pancreatectomy is favored for tumors in the body and tail. In the head of the pancreas, small, benign lesions require enucleation, and large or malignant lesions necessitate a Whipple procedure. The operative morbidity rate was 24%, and the mortality rate was 3.6%. The 10-year survival rate was 54.7% for nonfunctioning lesions, 68.4% for gastrinomas, and 92.4% for insulinomas. At this time surgery represents the only way to cure these lesions.