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.