Hypercalcemia — High Calcium Levels in Cancer

Hypercalcemia represents an oncological emergency defined by an elevated serum calcium level, frequently adjusted for albumin concentration. In oncology, it primarily arises via two mechanisms: humoral hypercalcemia of malignancy and osteolytic bone destruction. In humoral cases, tumours secrete parathyroid hormone-related protein (PTHrP), which stimulates widespread osteoclast-mediated bone resorption and promotes renal tubular calcium reabsorption.

In osteolytic hypercalcemia, direct skeletal metastases or myeloma lesions destroy bone matrix, releasing large stores of calcium directly into the extracellular fluid. The resulting hypercalcemic state impairs renal concentrating ability, precipitating dehydration, worsening electrolyte derangements, and causing progressive neuromuscular and cardiac toxicity if left uncorrected.

Hypercalcemia can develop rapidly and cause severe complications, including acute renal failure, cardiac arrhythmias, profound confusion, and coma. Recognising early symptoms allows clinical teams to intervene before organ function deteriorates. Because hypercalcemia frequently indicates advanced or progressive malignancy, identifying it prompt oncologists to re-evaluate overall disease control, review current systemic regimens, and initiate proactive supportive measures to protect quality of life.

Hypercalcemia is diagnosed using a standard blood test measuring total serum calcium alongside albumin, allowing calculation of albumin-corrected calcium (or direct measurement of ionized calcium). Diagnostic workup to determine the underlying cause includes measuring intact parathyroid hormone (PTH) to exclude primary hyperparathyroidism, parathyroid hormone-related protein (PTHrP), and vitamin D metabolites.

Hypercalcemia occurs in up to thirty percent of individuals with advanced malignancies. It is observed most commonly in multiple myeloma, breast cancer, renal cell carcinoma, and non-small cell lung cancer (especially squamous cell histologies). It also appears in head and neck carcinomas, urothelial cancers, and lymphomas producing excess 1,25-dihydroxyvitamin D.

Emergency therapy centres on vigorous intravenous hydration with normal saline to restore circulating volume and enhance renal calcium excretion. Intravenous bisphosphonates (such as zoledronic acid) or the RANK ligand inhibitor denosumab are administered to inhibit osteoclast activity and suppress bone breakdown. Calcitonin may provide temporary, rapid reduction, while loop diuretics are reserved for managing fluid overload.