Background
Ewing sarcomas (ESs) and primitive neuroectodermal tumours (PNETs)
exhibit identical genetic and histological characteristics, hence
collectively denoted as ESs/PNETs, originating from the neuroectoderm
and primarily consisting of primitive neuroectodermal cells. Primary
intracranial PNETs represent a rare, molecularly and clinically diverse
group of brain tumours, which is more common in children than in adults.
Though the appearance under microscope is similar to medulloblastoma
(MB), PNETs occur primarily in the cerebrum. They constitute 3-5% of
all paediatric brain tumours(1). The incidence of PNET in the United
States are 0.15 per 1 lac children aged 0 to 4, 0.05 among 5 to 9 years
old, 0.04 among 10 to 14 years old, and 0.03 among adolescents aged 15
to 19 years(2). They can be central PNET (cPNET) or peripheral PNET/ES
(pPNET), indistinguishable based on morphology, but having different
treatment and prognosis. Both of them can be differentiated based on
immunohistochemistry (IHC) and chromosomal studies including
Fluorescence in situ hybridization (FISH) and reverse transcription
polymerase chain reaction (RT-PCR). We describe two cases of
intracranial central PNET with negative IHC and chromosomal markers in
adult patients treated with craniospinal irradiation (CSI) and focal
radiotherapy boost with concurrent and adjuvant chemotherapy.