Lucca Holecliffe had an extremely rare tumour that had grown so big it was more than 10 per cent of the Auckland toddler's body weight.
Doctors said she had only 10 days to live and needed a lifesaving operation and blood transfusions.
Her parents, Jordanna and Jason Holecliffe, believe the surgery and the blood donors saved their daughter's life.
The little girl, who lives with her family in Forrest Hill on Auckland's North Shore, is now a happy, healthy 22-month-old.
They spoke to the Herald as the New Zealand Blood Service campaigns to get 10,000 new blood donors of types A and O.
The campaign launch yesterday - a take on a global drive - saw many leading New Zealand brands (including the Herald) lose the letters A and O from their online logos with no explanation, until today.
In February, Lucca's happy nature had gone. Her mum and dad noticed she had become clingy and difficult but at first blamed teething and travelling.
Her tummy looked big and she was off her food when they consulted a GP, who sent them to North Shore Hospital.
"They thought it was a twisted bowel, which was what we were expecting," Jason Holecliffe said.
"They sent us to Starship for an ultrasound. At 4am the ... doctor said, 'We think it might be a mass. It's probably malignant but we are not really sure'. We were shocked."
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Following a CT scan, a sample was surgically removed from the tumour which, 10 days later, was diagnosed overseas as EMIS - epithelioid myofibroblastic inflammatory sarcoma. The tumour, removed in a second operation, was enormous, weighing 1.1kg, more than a 10th of Lucca's 10kg bodyweight at the time.
EMIS is so rare it has been diagnosed in only about 10 people worldwide.
The wait for diagnosis had been a dangerous time.
"She was ... going downhill ... not interested in anything, not eating, losing weight," Lucca's mum said.
"The tumour was getting visibly bigger. Steve Evans, the surgeon, said [it had grown] since the biopsy. She would have had 10 days to live."
Last month, Lucca had a third operation, this one a minimally invasive keyhole surgery to remove a nodule from a lung because of concerns it may be cancerous. It turned out to be clear.
Jordanna estimates Lucca's blood transfusions have totalled up to four units of blood. She is now on the anti-cancer drug crizotinib, which her parents administer twice a day through a nasal-gastric tube.
She is doing well.
"She is an entirely different kid - happy and hopping around. She's grown heaps," Jason Holecliffe said.
Scans have indicated that more than 90 per cent of the tumour was removed and "they say they can't find anything bulky". But the future is uncertain.
"It's too early to say that it's gone completely."
Her mum said she and her husband were incredibly grateful for the anonymous blood donations that helped to save Lucca's life.
"I do remember thinking it would be nice if there would be some way they could hear that."
She said everyone should consider giving blood as it doesn't take long and is a great way to help others.