Primitive Neuro-Ectodermal Tumours (PNET) develop from cells that are left over from the earliest stages of our development, while we are still growing in our mother's womb as an embryo.
They occur in the brain or the spine, and can be divided roughly into supratentorial tumours and infratentorial tumors. This means above or below the tentorium – a membrane which separates the cerebellum from the lobes of the brain.
The infratentorial PNETs are far more common than the supratentorial PNETs. Infratentorial PNETs include medulloblastomas (which develop in the cerebellum) and pineoblastomas (which develop in the pineal region of the brain). Supratentorial PNETs include CNS PNETs.
They are more common in children and young adults. About 20-25% of childhood brain tumours are PNETs, which are high grade, fast growing tumours.
PNETs occur most frequently in younger children and incidence decreases with age with more than half of all PNETs being diagnosed in children less than 10 years old.
Nearly three-quarters (73%) of PNETs are medulloblastomas.
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