A new blood test being trialled could prevent the "blind" administration of chemotherapy for patients recovering from ovarian and bowel cancer.

To prevent cancer recurring patients often receive chemotherapy after surgery despite no indication of whether it's necessary.

Hugh McDermott was diagnosed with bowel cancer and had just come out of surgery to remove a large tumour.

He said the idea of not knowing whether to follow-up with chemotherapy was the most troubling part of his recovery.

"It's the uncertainty of not knowing which way to jump when chemo is being suggested, then having to have the treatment which would disrupt my life all over again," Mr McDermott told AAP.

Luckily Mr McDermott was eligible for the special blood test which showed his cancer was unlikely to recur, preventing unnecessary dosages of the anti-cancer drug.

"Christmas was coming up and I'd made travel plans, I felt greatly relieved that I was able to get on with my life," he said.

Led by Professor Jeanne Tie from the Walter and Eliza Hall Institute the new technology is being trialled across more than 40 hospitals in Australia and New Zealand.

The highly sensitive test looks for fragments of tumour DNA in a patient's blood which up until recently had been undetectable

Prof Tie described detecting these particular cancer cells in normal DNA like finding "a needle in the haystack".

Currently chemotherapy is offered to almost all bowel cancer patients to prevent the risk of cancer relapse.

"This is a real game changer for us because right now we are treating patients almost blindly," Prof Tie told AAP.

"Really only about 20 per cent of patients would actually benefit from the chemotherapy."

For recovering ovarian and bowel cancer patients who do show as high-risk of relapse, personalised doses of chemotherapy could be tailored accordingly.

After the trial began in 2015 'high-risk' and 'low-risk' groups were determined in early stage bowel cancer patients. It was then extended to women with ovarian cancer in 2017.

More than 400 patients have already joined but researchers are hoping to recruit upwards of 2000 by halfway through 2019.

Mr McDermott encourages others who are able to participate in the trial to sign-up.

"There is great advantage to gain from having access to information that could allay anxiety over the uncertainty in the future."

The study is expected to run until 2021 for bowel cancer and 2019 for ovarian cancer.