By the time the cancer was found it had spread to his stomach, requiring a major operation to remove a 2kg tumour, and now it has reached his liver.
Chemotherapy is expected to keep the cancer at bay for about another seven months, but after that his outlook is bleak. Specialists say his best chance of more time with his sons, aged 9 and 12, is an unfunded drug called Keytruda.
His family is now frantically trying to raise the $100,000 required. A Givealittle campaign has now raised more than $28,000; just last Thursday, when the Advocate ran an earlier story about Harris' plight, the total stood at $18,000.
Whatever happens, Harris and his whānau hope they will be able to help others by encouraging them to seek medical help early.
''We hope to spread awareness of bowel and colon cancer, among young people especially. A lot of them are going under the radar,'' he said.
Harris had always kept good health so when he was diagnosed he hadn't seen a doctor for about 10 years and didn't even have a GP. He never dreamt he'd get cancer at the age of 31.
Family spokeswoman Ruby Grace said it was important to see a doctor if something wasn't right.
''People can be whakamā (shy) because the symptoms of colon cancer can be a bit embarrassing. They don't want to see a doctor and say, 'I've had diarrhoea for a year', they just manage it. Our message is: Get seen, get checked.''
Since his diagnosis Harris said his family had learnt a great deal about cancer and cancer treatments, and wanted to share that knowledge with others going though similar experiences.
''We want to keep the ball rolling, even if I do pass on. It's not just us, there's lots of people suffering, and I feel sorry for them.''
Go to givealittle.co.nz/cause/from-graduation-to-hospital-gown if you want to donate.