In May Jaden Lee Stroobant was jailed for life for the crime, described in court as "callous and depraved".

Detective Sarah Cato is swimming the Waitemata Harbour this weekend to raise money for cancer charity Sweet Louise. Photo / Michael Craig

Cato is also instrumental in the ongoing investigation into the abduction and sexual assault of an 11-year-old boy in Ranui.

The boy was taken and assaulted after he got off a train at the Ranui Railway Station on November 17 last year.

Cato said giving up work while she had treatment was not an option.

"I'm a mother, first and foremost I wanted to be a role model for my daughter, I wanted her to learn resilience and teach her that no matter what you're dealt with you can push on through," she said.

"Operation Nepal was quite dear to my heart because I live in that community and my daughter attends school very close to the scene of the homicide - so I wanted to do the best I possibly could for the people who live in my community. 

"I wanted to give Madam Tian's family the best support I possibly could."

There is currently no cure for metatastic breast cancer and Cato is very realistic about that.

But it is treatable and she has vowed to do all she can to stay alive for as long as she can. 
"I am now being treated for quality of life, not quantity," she said.

Every three weeks she goes to hospital for her dose of Herceptin, a drug that targets metatastic breast cancer.

Every fourth and sixth week she is back for other treatments, and she takes hormone therapy drugs daily.

"I just push on with what I am doing," she said. 

"It doesn't matter how much it is - I've got a daughter and I've got to stay alive as long as I possibly can, so I'll do whatever that takes."

Cato said she doesn't dwell on her mortality and has never asked her doctors for a timeframe.

"Inevitably there are some dark moments with this diagnosis - but I don't focus on that at all, I've never had a timeframe, I don't want one.

"Some people with metastatic breast cancer live five years - there are others who have lived way longer and I am going to be one of those. 

"I've still got a lot of bad guys to lock up and hold accountable for their actions - and a lot of families to help.

Cato was then diagnosed with metatastic - also known as secondary - cancer, which is incurable.

"I have an opportunity every day to go into people's homes and make a difference, the best thing that I can do to help myself is to be helping others along the way. 

"Helping others also feels damn good."

Cato's determination to help others will see her swim across Waitemata Harbour this weekend to raise money for charity Sweet Louise.

Sweet Louise is the only charity in New Zealand that solely focuses on improving the quality of life for hundreds of women and men living with incurable breast cancer.

The charity currently supports almost 600 members around the country, offering information, advice, support and access to a range of practical and therapeutic services free of charge. 

"Ten years ago I had my daughter and I went swimming to lose the baby weight," Cato said. 

"I had a goal to do an ocean swim, but I was scared of sharks so I never completed it.

"Ten years on, I decided it was time, so I enrolled, then I thought if I was doing it I might as well do it for a charity."

Cato hopes to raise $15,000 for Sweet Louise.

So far her family, friends, colleagues and other cheerleaders have donated almost $4000.

The charity was a big support and help to Cato after her diagnosis, arranging a glamorous photo shoot with her close friends and daughter.

Detective Sarah Cato has been battling breast cancer for the three years. However, that has not stopped her doing her job. Photo / Michael Craig

"This charity is very dear to my heart and the work they do is so very special and valuable to its members."

Waitemata District Commander Superintendent Tusha Penny said Cato was "an incredible role model".

"Not only as a police officer who cares so deeply for the community she serves, or as an investigator who has tenaciously taken on incredibly complex investigations, but most importantly as a young mother who has been facing personal adversity with spirit and fight," she said.

"She has an incredible light about her and we feel lucky that she is part of our police family.

"She never looks for excuses, never looks for the easy option and is totally focused on helping others - even when faced with the biggest fight of her life.

"She's a hero." 

Support Sarah

To support Sarah's swim for Sweet Louise visit her Givealittle page here.

To donate directly to Sweet Louise click here or text GIVE to 2447 to for an automatic $3 donation.

Where your donations go:
• $10 means new members receive a welcome pack
• $20 means a member can attend a member meeting
• $30 means a Support Co-ordinator can visit a member at her home or hospital

For more information about Sweet Louise or metastatic breast cancer visit www.sweetlouise.co.nz

Breast cancer

In the early stages of breast cancer there is usually no pain and there may be no symptoms at all.

As the cancer grows, however, symptoms may appear, and need to be checked by your doctor.

Be alert for new lumps, changes in nipple or breast shape or size, and unusual pain which won't go away.

If you notice any of the following breast changes, it is very important that you show your doctor.

Monitoring yourself for abnormal breast changes and having regular mammograms once you're eligible means that, if you do get breast cancer, you're more likely to detect it early.

For information on how to check your breasts or if you have any concerns or questions, visit www.breastcancerfoundation.org.nz or call 0800 BC Nurse (0800 2268 773) to speak to an expert.