A father whose 5-year-old son was diagnosed with cancer has been stricken with terminal melanoma just as his only child has come to the end of his treatment.

Chris Sutherland's wife, Kelly, said her family's reality is now unimaginable but Lachie is helping his dad and giving him advice.

Kelly started telling their story online last year when the Christchurch family went to Australia for Lachie's treatment, but said she never imagined she would have to write about her husband's fight as well.

Lachie had fought his stage 4 neuroblastoma cancer well and the family started planning their first proper holiday, to Napier.

But two weeks ago Chris was diagnosed with advanced melanoma and doctors said he couldn't be cured.

"After 18 months of working tirelessly to get Lachie through his intensive treatment, to now be confronted with this new reality is unimaginable," Kelly wrote on Facebook.

"Chris is in good spirits and showing the same tenacity and determination as his son to not let cancer control his life. The past few days have shown that the apple has indeed not fallen far from the tree."

About three months ago, Kelly noticed a mole on her husband's back had become raised and urged him to see a doctor. A biopsy was done and the sunspot was removed "but it was fine", she told the Herald.

But following more tests, Chris was diagnosed with terminal melanoma. He's now in the care of Nurse Maude Palliative Care and the family is exploring options to extend his life.

Kelly urged everyone to get their moles checked and continue to do so.

When Lachie was diagnosed, Kelly started the TouchPauseEngage page to help her cope with their fight to make him well again.

She chose the name because it was an "obvious choice" for her rugby fanatic son who continued to play even through his treatment. Kelly called Lachie a "stoic and sturdy individual who just loves his rugby".

"I feel like we're in uncharted territory ... rather than needing to explain cancer to Lachie, he's offering Dad advice. It's a bizarre scenario to watch a 5-year-old comforting his father, and realising he's better equipped and qualified for the role than most of us." Kelly said going through her husband's diagnosis was "so familiar and yet so different".

"There is comfort in knowing that this feeling of drowning will pass, that strength and a determination to take control of the situation will soon follow," she posted a week after they received their second blow.

Kelly said they were surrounded by loved ones who had put their own lives and needs on hold, and donations and messages of support had come from far and wide.

"It's really so humbling and it really just restores your faith in humans," she told the Herald last night.

Excerpts from Kelly Sutherland's blog

July 5
I didn't envisage when I started this page that I would find myself having to share not only my son's cancer journey, but also my husband's, but unfortunately that has become our reality. On Tuesday Lachie's Dad was diagnosed with advanced melanoma and we have been advised that there is no cure.

July 9
A week can feel a lifetime, and it can pass in the blink of an eye ... this past week has been both. It seems impossible to comprehend that only a week ago Chris and I were looking forward to our first proper family holiday since Lachie was diagnosed to visit family in Napier, and at the same time this has been the longest, most exhausting week of my life.

July 15
So we are two weeks into Chris's diagnosis now and the fog seems to be lifting. With Lachie, there was the shock and grief, but we also had a very clear path to follow with regards to treatment protocol. This time has been quite different. Being sent home from hospital into the care of the Nurse Maude Palliative Care teams is fairly sobering. At the same time, the human instinct to survive is great and you're reluctant to accept that fate without asking a few more questions.

How to donate
www.givealittle.co.nz/cause/lachiechris