Malignant hypercalcemia is the most common metabolic emergency in cancer patients, occurring in 10-30% of advanced malignancies through three primary mechanisms: humoral hypercalcemia of malignancy (80%, mediated by parathyroid hormone-related protein [PTHrP] secreted by squamous cell carcinomas, renal, breast, and bladder cancers, which mimics PTH action on bone and kidney), osteolytic metastases (20%, direct bone destruction by metastatic tumor cells and osteoclast-activating factors in breast cancer, myeloma, and lung cancer), and calcitriol-mediated hypercalcemia (rare, from 1,25-dihydroxyvitamin D overproduction by lymphomas). PTHrP activates the same PTH1 receptor on osteoblasts, increasing RANKL expression that stimulates osteoclast-mediated bone resorption and calcium release, while simultaneously enhancing renal calcium reabsorption in the distal tubule. The nurse recognizes hypercalcemia symptoms using the mnemonic 'stones, bones, groans, and psychiatric overtones' (renal stones, bone pain, abdominal pain/constipation, confusion/lethargy), monitors calcium and albumin levels (correct for albumin: add 0.8 mg/dL for each 10 g/L albumin below 4.0), administers aggressive IV normal saline hydration (200-300 mL/hour initially), administers IV bisphosphonates (zoledronic acid) or denosumab, monitors for cardiac effects (shortened QT interval), and monitors renal function during treatment.