One in three Australians with newly- diagnosed bowel cancer would not act on genetic screening that showed predisposition to other cancers, researchers at the University of New South Wales (US) reported Tuesday.

Researchers from US Medicine took the extra step of screening for hereditary Lynch syndrome in 2,100 people with bowel cancer being treated at NSW hospitals over a three year period.

Lynch syndrome is an inherited disorder that increases the risk of many types of cancer. The researchers found that 245 of the patients in the study had a bowel cancer with features that suggested Lynch syndrome.

But 30 percent of the participants did not act on the results of their screening by giving a blood sample and their consent, and so the diagnosis of Lynch syndrome was missed.

"Even though we have the technology and the tools, there are very human reasons why people don't, or can't, participate," explained Robyn Ward, Head of the Adult Cancer Program at US's Lowy Cancer Research Centre.

"Some of the reasons were unavoidable -- people had mental health issues or language problems, or they died before they could agree," she added.

Diagnosis of Lynch syndrome is important for the management of the disease, as sufferers are recommended to have a colonoscopy every 18 months to two years -- so polyps and abnormalities can be identified and removed without surgery.

The hereditary nature of Lynch syndrome, meaning that first- degree relations may also be at risk, wasn't always enough motivation for people to take part in testing.

"Sometimes people agreed to genetic testing, but didn't want to know the outcome," said Ward.

"Like a young woman who tested positive for Lynch syndrome. Because we can't give her the results she can't give it to her family, either."

Nick Hawkins, co-author of the study and Head of the School of Medical Sciences at US, said no matter how accurate the tests are, they are as good as useless if not utilised or acted on.

"The tests we used on the bowel cancers in this study are very good, but they can't be of benefit unless individuals who test positive act on the results," said Hawkins.

"These new genetic tests are very powerful. But it's important to recognize the decisions and circumstances of patients can greatly reduce their usefulness in the real world. Both governments and funders need to understand this," he added.