This is caused by either of two mechanisms:

1. Humoral: in which the tumor (most commonly squamous cell, and renal carcinoma) produces something called parathyroid-related peptide (PTrP). You can guess what PTrP does from the name.

2. Bony metastasis: in which the cancer directly invades and erodes the bone (by producing osteoclast-activating factors) and thereby increasing the serum calcium levels.

To distinguish humoral hypercalcemia of malignancy (HHM) from HPT, all you need to do is to measure the level of PT hormone in the patient:

• if PT hormone is high, then it's HPT.
• if PT hormone is low or normal, then it's HHM (because HHM releases PTrP, not PT hormone).

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They are the most common cancers in infancy, and the most common extracranial cancers in childhood.
They are usually diagnosed before 5 years of age, and are classified into 3 subtypes:

• Neuroblastoma (malignant).
• Ganglioneuroblastoma (intermediate).
• Ganglioneuroma (benign).

MEN syndrome
(Multiple Endocrine Neoplasia syndrome)

MEN type-1

MEN type-2

MEN-2A

Familial thyroid medullary cancer

MEN-2B

The ganglioneuromas found on the lips and tongue in MEN-2B syndrome

Pellagra (vitamin B3, niacin, deficiency)