He bought a new boat as part of his "bucket list" and he and his partner Heeni Phillips are spending this weekend on the water.
"I am quite active and enjoying the good life."
He puts his unexpected improvement down to a new drug called Zytiga.
"It is not registered in New Zealand but I hope it will be. It has not been tested in New Zealand but it is approved in the US. It is very expensive. It costs $5000 a month but I'm paying $2500 a month," he said.
Williams will speak at the drug company Janssen-Johnson and Johnson Ltd conference in Auckland on Friday about his success story.
Phillips believes all men with prostate cancer should hear about this new drug. "Hopefully his story will encourage Pharmac to fund it and quickly - rather than dragging their heels," she said.
A Pharmac spokesman said a funding application was expected in the next couple of months but Medsafe needed to approve the drug first.
Late last year, Medsafe's Medicines Classification Committee recommended Zytiga be classified as a prescription drug, committee minutes show.
Medsafe clinical risk manager Chris James said Medsafe had completed an initial evaluation of the drug and was now waiting for the company to respond to a request for further information, which was made last month.
In Britain, cancer sufferers fronted a public campaign to get National Health Service funding for Zytiga. And in Canada, stage four prostate cancer sufferers and their families and friends have launched a petition to persuade provincial Governments to fund Zytiga.
But in New Zealand, such public campaigns have been controversial. It emerged last month that an emotional PR campaign in which terminally ill New Zealanders called for Government funding for the $500,000 a year "miracle drug" Soliris was funded by manufacturer Alexion Pharmaceuticals, a Nasdaq-listed firm that last year projected a net revenue of $1.35 billion from sales.
Williams also has had intravenous Vitamin C from an alternative medicine clinic in Remuera and electro pressure regeneration therapy from Graham Hayhow, the former All Black physiotherapist.
He swims 20 lengths at Auckland's Tepid Baths every day, eats a healthy diet and keeps positive.
"Cancer is a thing you have got to fight. You can't lie in bed feeling sorry for yourself. You cannot accept it. You have to do everything you can to combat it. You have to live each day and make the best of it," he said.
He has tried other forms of therapy.
When he was first diagnosed, his doctor recommended brachytherapy, in which radioactive seeds are implanted in the prostate gland. He suffered harsh side-effects and the cancer re-emerged.
He then had two rounds of radiation after the cancer spread to his spine and to nodules in his stomach.
Although covered by insurance, he has had to spend a lot of money on medication which is not covered, such as calcium injections at $1000 each.
