Former Prime Minister John Key offered up a stay at his multi-million dollar holiday home in Hawaii last night at a charity dinner trying to raise money for cancer treatment for Auckland detective Sarah Cato.

Last night at the black-tie event at the Trusts Arena in West Auckland more than $40,000 was raised towards the drug Cato is using to treat her metastatic breast cancer.

The elegant event, attended by 400 people, featured a string quartet, a band, a silent auction and a week's stay at Key's Maui house.

The drug, Perjeta, which the event was fundraising for, when used in conjunction with another drug, Herceptin, has been proven to reduce the risk of metastatic cancer worsening.

Cato, a 35-year-old mum of one, has been battling the disease with help of her wife, Keely, 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 her treatment with working full-time.

Along with being around for her wife, Keely, and daughter Emma, Cato says serving her community gives her a purpose to keep fighting for.

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 who didn't qualify for the funding."

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.

Cato said they had 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.

The Herald reported on Key's luxurious island home in Maui in 2009, when it was bought for $5.6m NZD.

"The 322sq m townhouse has a mini-bar and flat-screen TV in the master bedroom, three en-suite bathrooms, a Lani barbecue area with grill and outdoor fridge, a private lift, limestone floors, plush carpet and cherry cabinetry, and comes with luxurious furnishings and artwork."

Cato's Givealittle page can be found here, and remains open to donations.