The Whakatane toddler and his parents have been in London since March 21 and Chace has just undergone the first of four rounds of a $440,000 drug trial.
Chace's grandfather Rod Topperwien headed over to be with them late last week and Mrs Topperwien was talking to her family on Skype twice a day.
She said Chace had spent a night at their flat in the UK but was now back in hospital. He was okay but had an infection and doctors were trying to get his pain medication sorted.
Mrs Topperwien cried as she spoke of her only grandchild and the efforts her son and daughter-in-law were going to for him.
"They [Chace's parents] would have to be going through hell right now. They have told us time and time again they have to maintain positivity... Chace's condition can change every hour. He is such a tough little boy."
Mrs Topperwien said tests would be done in a few weeks to see if the bone marrow was improving and if it was then Chace would receive round two of the drug.
"If there is little improvement they won't continue with the next round. At the moment he is responding really well."
The Chace Topperwien Fundraising Facebook page has attracted 4193 followers. About $199,000 of the $440,000 needed for the drug trial has been raised so far.
"The community has been wonderful. They have really rallied and got behind us."
Rugby star Sonny Bill Williams was also going to be involved in fundraising for Chace.
Donations can be made at any ASB branch to the Chace Topperwien Fundraising account: 12 3217 0163111 00. For updates, visit the Facebook page or savingchace.com.