Bowel cancer rates rise in under-50s, calls for lower screening age

More young New Zealanders are being diagnosed with bowel cancer, in contrast to falling rates among older people. Screening will soon begin at 55 years old and researchers want it to start even earlier.

Adrienne Smithson felt that cancer was an older person’s disease.

The 45-year-old, from Hillcrest on Auckland’s North Shore, was until last year working as a primary schoolteacher and raising two daughters with her husband James. A long career and motherhood stretched out before her.

Then in July, she saw her GP for persistent pain in her stomach and after a series of scans was diagnosed with stage 4 bowel cancer.

“I never would have imagined getting cancer in my 40s,” she told the Herald. “It just came completely out of the blue.”

Smithson had no family history of bowel cancer or any of the known risk factors. She ate healthily, drank rarely and exercised regularly. She had health checks and blood tests after each birthday.

She also had none of the early warning signs of the disease, like rectal bleeding or problems with bowel motions. Instead, there was mild bloating in her stomach, then soreness in her abdomen. Scans later found they were caused by a tumour in her ovaries. Further tumours were found in her lungs and liver, all traced back to the bowel.

“It really wasn’t on my radar - just a huge surprise.”

The rising incidence of colorectal or bowel cancer among younger people is a global phenomenon and was first noticed in New Zealand around a decade ago.

A new study published today by University of Otago researchers showed that cases among under-50-year-olds grew by 26 per cent on average per decade between 2000 and 2022.

“That’s a higher rate than we originally thought,” said Professor Frank Frizelle, a colorectal surgeon, advisor to Bowel Cancer NZ and co-author of the study. “And it’s accelerating. So the rate of increase is increasing.”

The increase among Māori under 50 years old was even higher, at 36 per cent.

Lead author of the study Dr Oliver Waddell, a surgical trainee and PhD candidate, said this was “of grave concern” because Māori were more likely to die from the disease than non-Māori, and were more likely to be diagnosed with advanced cancer - possibly because of delayed diagnosis and inequitable access to cancer treatment.

Part of the problem could be that younger people were navigating a part of the health system designed for older people. Doctors were not accounting for the changing nature of bowel cancer and young patients with symptoms were not seeking help.

The findings underlined the importance of lowering the bowel screening age, the researchers said. Over the study period, cancer rates fell 18 per cent among 50- to 79-year-olds - likely because of screening which begins at 60 years old.

The National-led Government has committed to lowering the screening age to 55 years old. Waddell said it should fall much further, to 45 years old.

The screening age for Māori and Pacific patients - which is currently 50 because these groups typically get bowel cancer younger - should drop to 40 years old, they said.

Most comparable countries screened at 50, though Australia allows people to request screening from age 45. In the US, the recommended screening age was changed to 45 in 2021.

Lowering the age further in New Zealand would require significant workforce increases to deal with more colonoscopies and surgeries. There are already concerns about the health system’s capacity to cope with the drop from 60 to 55.

Prime Minister Christopher Luxon first made the commitment to a lower screening age when put on the spot in a pre-election debate last year.

Health Minister Shane Reti said in a statement that improving cancer - including better prevention and early detection - was a priority for the Government.

“As was the case with the announcement to raise the age of breast screening, any decision to adjust eligibility for screening has significant clinical, workforce and funding implications to consider.”

Reti has received advice from the Ministry of Health on lowering the screening age. His office declined to release it to the Herald on the grounds that it was under active consideration.

Little is known about what is driving the rise in younger bowel cancer rates in New Zealand and worldwide.

Dr Frizelle said it was increasingly clear that it was not driven by genetics but by environmental factors.

The typical risk factors for bowel cancer were diet, exercise, and rurality. Yet younger New Zealanders were now eating less meat and drinking and smoking less, and cases were more likely to be in urban areas.

One of the theories is that microplastics might play a role, possibly by damaging the mucus layer that protects the bowel lining. The impact of changing diet and growing body sizes were also being investigated as potential drivers.

Isaac Davison is an Auckland-based reporter who covers health issues. He joined the Herald in 2008 and has previously covered the environment, politics, and social issues.