Administrative Officer of Acharya Harihar Regional Cancer Research Centre, Prashant Mishra said the fire broke out in the store room in the third floor of its new building at around 5 pm.
The boy, identified as Samuel Behera and hailing from Talcher, died while being evacuated along with 79 other patients from the building.
"The boy died during shifting and not in fire," Mishra said adding none was injured in the incident.
The building, which was inaugurated six months ago, also houses the operation theatre.
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Electrical short-circuit could be the reason behind the fire, they said.
District collector N C Mishra rushed to the spot and supervised the evacuation of patients and continuation of their treatment at a makeshift ward.
He ordered an administrative probe to ascertain the cause of the mishap which has caused extensive damage to the building.