Brave Oliver Stephenson, 5, was finally given the all-clear earlier this year after battling neuroblastoma, a rare cancer originating from immature nerve cells, throughout 2020.
As the super schoolboy underwent chemotherapy, surgery, stem cell treatment and a bone marrow transplant, his loved ones desperately crowdfunded for financial support.
At one point, Oliver and his dad James, 33, had to isolate together in a 15sqft hospital room in Leeds General Infirmary for seven weeks because of the coronavirus pandemic.
The family watched on in amazement as kind-hearted strangers donated a staggering £270,000 which they have used to fund his place on a medical trial.
Oliver has spent the past month at New York s Memorial Sloan Kettering Cancer Center, where he is on a clinical trial vaccine called bivalent.
It is hoped the treatment will train his immune system to identify and destroy neuroblastoma cells lurking in his body, to prevent the disease from ever returning.
The vaccine, which costs £210,000, will require the youngster to make four more trips across the pond this year.
He returned from his recent four-week trip to The Big Apple around a week ago with his mum Laura, dad James and little brother Alfie, 3.
Laura, 35, said: "Everything went great. The doctors were all amazing and Oliver has responded well so far.
"It is a clinical trial so we don't know what will happen but we are hoping that this will prevent Oliver from suffering as he has done again.
"After everything he has been through it feels great to be on a positive track."
She added the treatment was "quick and easy", explaining Oliver had three vaccines, which were given via jab, and that other than some discomfort he had no obvious side effects.
Due to the length of their stay, Laura said the family were able to make a holiday out of the trip.
She added: "Oliver and Alfie had a brilliant time in New York, it was amazing.
"Because of the pandemic everywhere was really quiet, which meant we felt very safe all the time and didn't have to queue for anything."
Laura, who lives with her family in Wakefield said Oliver's favourite part of New York was Central Park and playing in the playgrounds there.
The pioneering treatment comes almost 18 months after Oliver was diagnosed with neuroblastoma, a rare cancer originating from immature nerve cells that affects only 100 children annually.
The family's ordeal was worsened by the Coronavirus pandemic, which meant Oliver and James had to isolate in together in hospital while the youngster had chemotherapy.
James was at his son's bedside throughout but Laura and Alfie were unable to visit due to restrictions and had to make do with video calls.
Crowdfunding pages were set up to help the family pay for treatment once options on the NHS were exhausted, as neuroblastoma has a significant chance of returning.
Laura went on: "The incredible support and donations not just from our friends and family but around the world has been overwhelming.
"We are so grateful to everyone who has helped.
"It's been a really difficult year for us and back in 2020 Oliver's prognosis wasn't good at all.
"But he has battled through everything is doing well now, he's fit and strong and even back at school.”
Despite Oliver getting the all-clear, figures show 60% of people who recovered from neuroblastoma end up relapsing.
Laura added: "We want to everything we can to stop that happening."
Throughout Oliver's ordeal, his family has been supported by the Solving Kids Cancer charity.