In addition to pancreatic NET-related ACTH ectopic secretion (causing Cushing’s syndrome) [121,167], tumor-related high calcium levels are caused by PTHrP (parathyroid hormone-related peptide) overproduction that suppresses PTH levels during negative feedback via serum calcium (in patients with intact parathyroid glands) [168,169]. Here, PTH is linked to Cushing syndrome.