New NHMRC guidelines put age and family history up front and centre in determining who should be screened for bowel cancer with colonoscopy and who needs iFOBT.

It has been known for some time that family history can influence the risk of developing bowel cancer, Australia’s second most common cause of cancer death. But it is also known that specific, identified genetic mutations causing conditions such as Lynch syndrome or familial adenomatous polyposis are rare, accounting for less than 5% of all bowel cancers diagnosed. At most, the researchers say, this only explains half of the reasons why family history is a risk factor for bowel cancer.

“The remainder of the observed increases in familial risk could be due in part to mutations in yet to be discovered colorectal cancer susceptibility genes, polygenic factors such as single-nucleotide polymorphisms, or dietary and other lifestyle factors shared by family members,” the guideline authors said in the Medical Journal of Australia.