About four weeks ago Haines, 45, went to the doctor because it felt like he had something in his throat.
At first the doctor was not concerned but when his throat started to become painful and he was struggling to eat, the doctor sent him for an endoscopy.
It showed an ulcerative lump in his throat which doctors later confirmed was an HPV cancer which most likely started in the bottom of his throat (hypopharynx) and spread to his voice box (larynx).
Haines, who also composes, produces and DJs, has already had two operations to remove some of the bulk of the tumour which was clogging his throat and today had surgery to remove some of the lymph nodes around his throat and a quarter of his larynx.
"If they take too much, I might lose my ability to swallow. I might lose my voice," he told the Herald before his surgery.
But despite the risks and having to cancel all his shows over the busy summer months, he remained positive.
The first two surgeries had been a success – he could hardly talk two weeks ago but had his voice back and playing his saxophone felt much better once part of the growth was removed - and he was confident today's big operation would be as well.
"For me, something like this might have been my absolute worst nightmare, to lose all my earnings and at the busiest time of year, but I knew something was wrong about six months ago. It was a relief [to find out what]," he said.
"I'm just seeing this whole new side of life. I've probably been a very selfish person. Life for me has always been a fight. I have to fight to be successful.
"When I'm better and on my path to recovery I'm going to have a whole new outlook on life.
"You really start finding out about what's important. The most important thing in my life three months ago was trying to raise money to put an album out. Now I'm totally on the other side of the situation. I've got no income and I'm just about to go into hospital but, in my mind, I feel so much better. I was driving myself into the ground.
"Being around and seeing my son grow has been the most amazing thing in my life."
Haines, who has played with musicians including US soul legend Marlena Shaw and Jamiroquai, said he had been living life at "break-neck speed" and becoming unwell had reminded him he could not keep living that way.
While he was determined to slow down and focus on what's important in life one he recovered, he still planned to put another album out. "I'll be going guns blazing to do that," he said.
Doctors told him he had a very good chance of making a full recovery but would need a couple of months of radiotherapy following the operations and possibly even chemotherapy.
Haines, his wife and their three-year-old son Zoot, who all moved back from London two years ago, lived show to show like many entertainers, so having to cancel all his gigs was putting financial pressure on the family and had prompted a Givealittle page to be set up.
But even without the page Haines said he had been amazed by all the support he had already had.
"I just want to thank the people who are helping us at this very challenging time for our family."
Nathan Haines
• The eldest son of jazz bassist Kevin Haines
• Grew up on Auckland's North Shore
• Won New Zealand's Tui Jazz Album of the Year award three times, most recently in 2014
• Has released 10 albums between 1994 and 2015
