When used in conjunction with another drug, Herceptin, Perjeta has been proven to reduce the risk of metastatic cancer worsening.
Cato, a 35-year-old mum of one, has been battling the disease since her diagnosis four years ago.
She underwent a mastectomy, but soon afterwards her doctors discovered the disease had spread and was metastatic, or incurable.
The years following have involved a gruelling course of chemotherapy, radiation and rounds of Herceptin.
Work on several high-profile criminal investigations has been punctuated by frequent trips to the hospital, and Cato continues to juggle working full-time with her treatment.
Along with being around for her wife, Keely, and daughter Emma, Cato says serving her community gives her a purpose to keep fighting for.
Speaking to the Weekend Herald at her West Auckland home in the lead-up to the event tonight, Cato says the event isn't just about her own fight for life.
The gala is a celebration, she says, of a community "coming together and supporting each other".
"Cancer is something which unfortunately affects everyone in society, in one way or another," she says.
As well as celebrating the community around her, Cato says the event is about raising awareness about the situation she, and many others, face.
Perjeta became fully funded by Pharmac at the start of last year - but only for patients who had not been previously treated with Herceptin or chemotherapy.
"Because I was diagnosed four years earlier I don't qualify for funding," Cato said.
"There was, last year, 160 of us that didn't qualify for the funding."
"Now, only a year later, there's 128. People can read between the lines in where those other, unaccounted for people have gone."
Cato sees the treatment, which she described as "gnarly", as being crucial for her to be around for Keely and Emma.
However, it comes with an almighty price tag.
A round of Perjeta is administered every three weeks, at a cost of $7000.
Since the West Auckland detective appealed for public help, more than $124,000 has been donated through a Givealittle page. The first $100,000 was donated in the week after the Herald first shared Cato's story.
But Cato is very aware of the rate at which the treatment exhausts the funds being raised, and the constant need to top this up.
The fundraising goal for the night is open - as Perjeta is a "pay as you go scheme" Cato says there isn't a set target.
"We're almost at that target of $150,000 (for the first 18 months of treatment) and then of course it's about $40,000 every year after that as well.
"So we're not capping it."
Cato's wife Keely says the little family is hugely grateful for the influx of support they have received to help Sarah access the drug.
"We were talking about getting Sarah on the treatment about a year ago, but with that sort of money it just seemed like too daunting of a task," she said.
The pair have been flat tack all week organising tonight's event - moving wine, writing thank-you cards and mapping out seating plans.
Broadcaster Simon Dallow is hosting the event alongside comedian Urzila Carlson.
Cato says they have been "very fortunate" with donations for the silent auction - which included experiences like heading out on to Auckland's harbour with members of Emirates' Team New Zealand.
She has crafted a video of her journey over the past four years to show the crowd in lieu of a longer speech, but will also share a few words at the event.
Keely says today will involve a bit of pampering. A family friend will do their hair and they were also planning on popping into a Bobbi Brown kiosk to get their makeup done.
Cato has a special outfit planned for the event and will be sporting some special jewellery for the occasion - earrings given to her when she qualified as a police officer around eight years ago.
Cato is part of a closed Facebook group set up for women fighting metastatic breast cancer, which she says is the site of much discussion about the injustice of the issue.
She hopes tonight's event will bring this injustice into the spotlight.
"We're making a little bit of noise about that - we're getting just a little bit rowdy."
Cato's Givealittle page can be found here, and remains open to donations.
