Humoral Hypercalcemia of Malignancy

Sam Kessler is a 69-year-old retired businessman. He and his wife had been looking forward to spending more time with their children and grandchildren. Unfortunately, 3 years ago, Mr. Kessler was diagnosed with lung cancer. Despite surgery, radiation therapy, and chemotherapy, his cancer returned. Mr. Kessler told his physicians that he did not want further treatment and preferred to spend his remaining time at home with his family, as pain free as possible. In the past week, Mr. Kessler became very lethargic and had both polyuria (increased urine production) and polydipsia (increased water drinking). He was admitted to the hospital, where laboratory tests were performed (Table 69).

During a test involving 4 hours of water deprivation, Mr. Kesslers serum osmolarity was 305 mOsm/L (normal, 290 mOsm/L) and his urine osmolarity was 90 mOsm/L. The physicians concluded that Mr. Kessler had humoral hypercalcemia of malignancy because his lung cancer cells were secreting parathyroid hormone (PTH)-related peptide (PTH-rp). He was treated with a saline infusion and furosemide (a loop diuretic), which caused his serum Ca²⁺ to decrease to 10.8 mg/dL. He returned home with a prescription for pamidronate, an inhibitor of bone resorption that was expected to keep his serum Ca²⁺ in the normal range.