This document discusses malignant hypercalcaemia, which occurs in 10% of cancer patients and is caused by bone metastases or humoral factors released by tumour cells. It leads to high calcium levels in the blood (>3.0 mmol/L) and poor prognosis, with most patients dying within a year. The document outlines the physiology and clinical manifestations of hypercalcaemia and provides recommendations for investigations and management, including rehydration, calcium restriction, bisphosphonates, calcitonin, and targeting the underlying malignancy.