PTHLH and Hypercalcemia: O. Burzyantseva et al. [143] hypothesised that the secretion of haematopoietic factors, such as G-CSF, PTHrP, IL-1, etc., would trigger the release of leukocytes that subsequently act on the common precursors of osteoclasts and granulomonocytic cells to cause hypercalcaemia.