MEN1 is characterized by: 1) adenomas of parathyroid/adenomas of parathyroid (affecting over 90% of patients by the age of 50 and causing primary hyperparathyroidism (PHPT), which can be associated with hypercalcemia); 2) adenomas of adenohypophysis (mainly prolactin-secreting adenoma or, more rarely, non-functioning macroadenomas); 3) neuroendocrine tumors of gastro-entero-pancreatic tract (GEP-NETs) [1]; (Table 1). This evidence concerns the gene MEN1 and hypercalcemia disease.