This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Physiology
A 88 year-old woman from Mexico is admitted to the hospital following a bout of severe vomiting and generalized weakness. Initial laboratory values reveal elevated Cat levels. The referring physician tells you that she has breast cancer and her bone scan indicates metastasis to bone. The most likely cause of hypercalcemia is: 
Select and explain. 
A. Increased PTH production, B. Increased responsiveness of the PTH receptor 1, C. Increased PTHrP production, D. Decreased responsiveness to calcitonin
C: Increased PTHrP production
Answer: C: Increased PTHrP production 
Explanation: Increased PTHrP productions