- Is caused by PTH-related peptide (PTH-rp) secreted by some malignant tumors (e.g., breast, lung).  PTH-rp has all of the physiologic actions of PTH, including increased bone resorption, increased renal Ca2+ reabsorption, and decreased renal phosphate reabsorption.
- Is characterized by the following:
a) increased serum [Ca2+] hypercalcemia
b) decreased serum [phosphate] (hypophosphatemia)
c) increased urinary phosphate excretion (phosphaturic effect of PTH-rp)
d) decreased serum PTH levels (due to feedback inhibition from the high serum Ca2+)