PTH and Hypercalcemia: The most common cause of hypercalcemia in various cancers (lung, renal cell, ovarian, thyroid, colorectal, breast cancer, hepatocarcinoma, cholangiocarcinoma, neuroendocrine, and gastrointestinal stromal tumors) are the alterations of PTH levels and release of cytokines (osteoclast stimulating factor) from the tumor.57