"We want more than months and that is why we have chosen to seek further treatment in Germany.
"Immunotherapy has been available in Germany for many years and is making advances in cancer treatment."
The alternative treatment could not be given in New Zealand or Australia because of legalities and had not been trialled in either country for long enough to gain official approval.
However, Mrs Gunter said she believed it would give Mike a far better chance of "living longer".
"We will be travelling to Germany at the end of February, after Mike has undertaken radiotherapy and chemotherapy here.
"It will be a two-pronged attack and the doctors in Germany told us to do the radiation and chemotherapy before we left, which would allow the immunotherapy to work more effectively.
"If there is a chance, we are going to give it a go anything is better than nothing."
The tumour, a glioblastoma multiforme grade four, has been removed, but Mrs Gunter said because it was an aggressive type of cancer, it remained in Mike's blood vessels.
An online Givealittle page has been set up to help the family finance the $150,000 treatment and trip to Germany. Last night, 181 donors had given $15,244.
"People are just amazing and the support they have given us is tremendous," Mrs Gunter said.
Mike was a fit and healthy young man, and a fighter, she said.
"No one has promised us a cure, we are fighting for a longer life for Mike."
To donate go to: https://givealittle.co.nz/cause/helpmikewinthisfight/