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How gene testing can help cancer-susceptible families

Detection of an inherited genetic mutation that raises cancer risk can be a lifesaver.

Mary Bradley was only 28 when she was diagnosed with stage three bowel cancer. Looking back, she’d had some symptoms – she was exhausted, anaemic and had experienced a change in bowel movements – but put them all down to being the new mum of a six-month-old boy.

“Then I found a lump and thought it was a hernia and was very close to not going to see my GP, but my husband encouraged me,” she recalls.

Thankfully, her doctor recommended tests and the aggressive cancer was caught while it was still treatable. Twelve years on, Bradley now has confirmation that her chances of cancer were always higher because she has Lynch syndrome. This genetic condition is among the most common inherited cancer syndromes. There are more than 500 families in this country who are registered as having it, and potentially more who are undiagnosed.

Lynch syndrome increases the risk of developing a range of cancers but, in particular, cancers of the bowel, womb and ovaries. For Bradley, it has been passed down through the generations – her grandfather died of bowel cancer and her father has had it, too. Since there is a 50% chance that a child will inherit the genetic mutation, she is facing the fact that she may have passed on Lynch syndrome to her three sons.

“They won’t be tested until they’re 18 and I’m hoping they won’t have it,” she says. “Still, it’s better that they know, as it may save their lives.”

Mary Bradley. Photo/Lee Howell/Supplied

Lynch syndrome involves mutations in the mismatch repair genes. Christchurch colorectal surgeon Chris Wakeman describes it as like an error in the spellcheck function of a computer. Normally, when cells grow and divide, minor mistakes occur and the repair genes are able to recognise and fix them. People with Lynch syndrome lack the ability to repair mistakes and, as they accumulate, this can lead to cancer developing.

As genetic science has developed, we have become better at identifying the different variants of Lynch syndrome. Samples from bowel cancers in New Zealand are now examined to rule it out. If changes are found, or if an individual has a strong family history of bowel cancer, and particularly where it is occurring in younger people, gene testing is offered.

Some are reluctant to get tested, in case it affects their health and life insurances. A positive result also has consequences for a person’s extended family, who will also have to be tested, which can lead to guilt and sensitivity.

But being armed with the knowledge means those with the syndrome can take preventive action such as having yearly colonoscopies so any polyps on the bowel can be removed before they have a chance to develop into cancer. And those with the syndrome who want to have children can take up the option of pre-implantation diagnosis to avoid passing it on, taking advantage of three funded fertility-treatment cycles.

Gene testing has strict criteria, says Wakeman. “What we really want to avoid is people using services such as ancestry.com. You sign up and get tested to see if you’re part-Viking and for an extra fee you can be tested for your health genes.

“But it’s not a verified lab and there’s no counselling or advice; they just say you have the gene. They might get the genetic defect right but, since they don’t have access to the database, they can’t check how significant a mutation is.”

Not everyone with Lynch syndrome is going to get cancer, but it increases the chances. For instance, there is a 50% chance of developing bowel cancer, as opposed to the average New Zealander’s 6%, and it is likely to occur earlier. And, for women, there’s a 30% or greater chance of getting womb cancer, as opposed to less than 2%.

Bradley has opted to have a preventive hysterectomy. “I was a bit reluctant to do it because of all the surgeries I’ve already had, but it was such a high risk,” she says.

As one of the founding members of Bowel Cancer NZ, she is keen to raise awareness of Lynch syndrome.

She says it is important to know your family’s medical history and, if necessary, get gene-tested so you can be regularly screened for any cancers you may be predisposed to.

“Our family feels fortunate to be in a position where we can make sure everyone is screened,” she says. “Fifty years ago, we would have been one of those families where people died really young.”

This article was first published in the November 23, 2019 issue of the New Zealand Listener.