Most common cause of hypercalcemic crisis is -

<p>Hypercalcemia due to malignancy is common (occurring in as many as 20% of cancer patients, especially with ceain types of tumor such as breast cancer), often severe and difficult to manage, and, on rare occasions, difficult to distinguish from primary hyperparathyroidism. Although malignancy is often clinically obvious or readily detectable by medical history, hypercalcemia can occasionally be due to an occult tumor. Previously, hypercalcemia associated with malignancy was thought to be due to local invasion and destruction of bone by tumor cells; many cases are now known to result from the elaboration by the malignant cells of humoral mediators of hypercalcemia. PTHrP is the responsible humoral agent in most solid tumors that cause hypercalcemia(harrison 18 pg 3106)</p>