"We were pretty messed up for a while," Mr Topperwien said. "We went from everything going really well to basically just a few weeks to live."
The couple quit their jobs and took their only child home to family in Whakatane, carrying on as normally as they could for their little boy, and packing as much fun as possible into each day.
At the time Chace showed no signs of the battle going on inside his body. His hair had grown back, and he ate, slept and played just like any other youngster.
And even when the disease began progressing last week and Chace was racked with pain and 42-degree temperatures, Mr Topperwien said his son put on a brave face.
"I asked him if he was okay and he said, 'Yes Daddy, I'm good.' If he isn't prepared to give up fighting then neither are we."
The Topperwiens spent hours trawling the internet and two weeks ago they found a promising new drug trial in Britain.
The drug blocks the activity of a group of proteins called aurora kinases that control cell growth, thereby inhibiting the growth of cancer cells.
Chace was accepted on to the phase one trial and after a false start at the weekend, when his illness prevented the family from flying on his third birthday, the trio are now preparing to leave New Zealand tonight.
Mrs Topperwien said that although she and her husband were realistic about the low chance of the drug curing their son, they were hoping to buy Chace precious time until he could receive a second bone marrow or stem cell transplant.
"This is a long shot and we know the odds of this aren't necessarily in our favour. However, we have no other option at this stage."
A second transplant within a year could kill Chace, which means they have to wait at least four months before the treatment can be attempted again.
"I ask myself, 'What would Chace want me to do?' and I reckon that he would want us to fight to the very end, just like he has, so that is exactly what his Mummy and Daddy are going to do," Mrs Topperwien said.
But there are catches.
The trial cost was originally $120,000 but yesterday the family were dealt another blow when a new figure came in at $423,000.
They hope to negotiate the new cost down and will use $69,000 raised for them last year by family, friends and the public for this type of emergency, but they will still come up short.
Now they have no choice but to rely on the same group to keep the fundraising going while Chace is on the trial, which could last up to four months.
More importantly, they are desperate for more Maori and Pacific Islanders to become bone marrow donors.
With no bone marrow match in the world for Chace out of a register of more than 8 million people, the Topperwiens hope to raise awareness in an effort to boost the Maori and Pacific Island register of 500 donors so there is a potential match for their son after the drug trial.
Now the family are praying for a miracle.
Donations to help Chace can be made at any ASB branch to the Chace Topperwien Fundraising account, number: 12 3217 0163111 00. For updates visit the Chace Topperwien Facebook page by searching his name.
RARE CANCER
What: Acute myeloid leukaemia is a cancer of the blood-forming tissue in bone marrow.
Trial: Using drug that blocks activity of proteins which control cell growth.
Cost: Between $120,000 and $423,000.
Aim: To keep Chace alive long enough to have a second bone marrow transplant.
Need: More Maori and Pacific Island bone marrow donors.
