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:
Increased PTHrP productions
Increased PTH production
Increased responsiveness of the PTH receptor 1
Increased PTHrP production
Decreased responsiveness to calcitonin