First, in some humoral syndromes, causative factors are now identifiable; the condition of humoral hypercalcaemia of malignancy (HM) is a good example. Hypercalcaemia develops in approximately ten per cent of patients with advanced stages of cancer, and it is now established that a newly discovered calcium-regulating hormone, parathyroid hormone-related protein (PTHrP), is the causative factor in almost all patients with HM.
