This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Endocrine System, Subject name: Physiology
Hypercalcemia associated with malignancy is most often mediated by: 
Select and explain. 
A. Parathyroid hormone (PTH), B. Parathyroid hormone related protein (PTHrP), C. Interleukin - 6 (IL-6)., D. Calcitonin
B: Parathyroid hormone related protein (PTHrP)
Answer: B: Parathyroid hormone related protein (PTHrP) 
Explanation: PTHrp was discovered as a product of human cancers that are of squamous cell origin and that are associated with hypercalcemia. However, normal tissues also express this protein - skin keratinocytes, lactating mammary epithelium, placenta, and fetal parathyroid glands. The gene for PTHrp and for PTH is on paired chromosomes. PTHrp binds to PTH receptor; it exhibits most of the actions of PTH on bone and kidney. Hence, it produces hypercalcemia. One action of PTH NOT shared by PTHrp is: stimulation of renal 1-hydroxylase. Hence, patients with hypercalcemia caused by PTHrp do not have elevated 1,25-dihydroxycholecalciferol. The most impoant physiological role of PTHrp is regulation of endochondral bone formation .