Colorectal cancer: What are the symptoms and why are cases in younger New Zealanders rising?

The rates of early-onset bowel cancer are rising in New Zealand.

More than 3000 people are diagnosed with colorectal or bowel cancer in New Zealand each year, and more than 350 of them are under the age of 50. More than 1200 will die from it.

It may be more common in those aged 50 and over, but it can affect people of all ages.

Married At First Sight Australia expert Mel Schilling died of colon cancer at 54, her husband announced this week. Schilling was first diagnosed in 2023, when she was 51, and the cancer eventually spread to her lungs and brain.

Kiwi comedian Dai Henwood was diagnosed with stage 4 incurable bowel cancer in 2020, at age 42. And Dawson’s Creek star James Van Der Beek, 48, recently died from the disease.

In New Zealand, the rates of early-onset bowel cancer are rising, increasing by about 26% per decade in the general population and by more than 30% among Māori.

Experts are calling for the eligibility age for free bowel screening to be lowered to 45. This month the age is being lowered to 58 from 60 across the rest of the North Island after this was done in Northland, Auckland and the South Island in October.

What are the signs and symptoms of colorectal cancer?

Colorectal cancer is the clinical term for cancer of the colon or rectum, commonly known as bowel cancer.

Symptoms can include rectal bleeding, anaemia, severe abdominal pain, a lump in the abdomen, changes in bowel movements, fatigue or weight loss for no apparent reason.

“Early-onset cancer tends to be a left-sided disease, which means it tends to affect the rectum and the sigmoid [colon],” colorectal surgeon Dr Frank Frizelle says.

“Tumours in the rectum and sigmoid are more likely to present with rectal bleeding and increased rectal mucus and increase in frequency of defecation, which is associated with almost normal stool.

“Right-sided tumours tend to present more subtly – with anaemia, fatigue, a lump in the tummy, loose stool as opposed to formed stool and not so much overt rectal bleeding.”

What causes colorectal cancer?

Frizelle says about 1% of bowel cancer is associated with chronic inflammatory diseases like ulcerative colitis or Crohn’s disease.

“About 10% of people have an inherited genetic condition that increases their chance of getting bowel cancer. In younger people it accounts for a higher percentage, because if you’ve got an inherited genetic condition, you tend to get bowel cancer at an early age.”

These conditions are related to mismatch repair gene abnormalities like Lynch syndrome, or FAP (familial adenomatous polyposis) – genetic mutations that lead to cancer developing.

Most bowel cancer – 90% – is sporadic. “It just happens. That is largely driven by environmental conditions – the combination of the bacteria in your gut and the food you eat.”

What role do gut bacteria and diet play?

Your gut bacteria is mostly inherited from your mother, and interacts with what you eat. Some types of gut bacteria produce toxins that damage cells and produce pre-cancerous lesions.

One of these bacteria, Enterotoxigenic Bacteroides fragilis, makes “more toxin in the presence of red meat and less toxin in the presence of fibre and vegetables”, Frizelle says.

“That fits with what we know epidemiologically, that people who eat a lot of red meat are more likely to get bowel cancer.

“So what we think causes sporadic bowel cancer is related to your diet and having certain bacteria in your gut that make toxins. Those are controlled by what happens in the early part of life.”

Your gut bacteria can change with your environment and diet at an early age, he says. For example, if you migrate as a teenager from a low-risk to a high-risk Western environment and diet, or from a rural to an urban setting, your gut bacteria changes for the worse.

“That’s not unlike what we know about sun damage in skin. It’s not when you’re 60 and get your sunburnt nose that causes your skin cancer, it’s when you were 16 and got out there and got sunburnt, and it’s 50 years later that the cumulative injury has occurred.”

What can increase or decrease your risk of getting colorectal cancer?

Risk factors for colorectal cancer include being 50 or older, a family history of bowel cancer, eating too much red and processed meats and animal fats, and not getting enough fruit and vegetable fibre.

Alcohol, smoking, obesity and a lack of exercise also increase your risk.

You can lower your risk by eating a healthy diet, reducing fat and saturated fat intake, limiting red and processed meats, and exercising regularly.

Why are cases rising among younger people in New Zealand?

Research is being done to work this out, Frizelle says.

“If our model is right, the bacteria is lying inside you and then the food’s coming in, making toxins, causing damage.”

However, young people today eat less red meat and more vegetables, and drink and smoke at lower rates than in previous decades.

“Something else environmental is altering the balance and causing something to change.”

The colon has a protective mucus layer that stops toxins from doing damage. It may be that processed foods, sugary drinks or microplastics are damaging it, Frizelle says.

“Not that the plastics themselves are causing the cancer, but they may damage the mucus layer or work as an agent to carry the toxins.

“Why things have changed we don’t know – we know it’s environmental, what it is in the environment we don’t know."

While bowel cancer cases are increasing in over-50s, they have stayed the same in the 80-and-over age group. In the 60-80 age group, they are decreasing.

“[This is] largely due to screening, a lot of people having colonoscopies for rectal bleeding, and increased awareness,” Frizelle says.

“It’s not that people 60 to 80 are leading a better life, it’s just that they’ve got a high level of intervention.”

For a third of people under 50 with bowel cancer, the disease is incurable by the time they present to a doctor. That can be because they don’t recognise they have a problem, because symptoms can come and go.

“It means there’s a delay in patients recognising that they’re not well. Secondly, the health structure is inevitably difficult to get through. GPs and the public system are focused on looking for [this in] older people.

“So if you’re 65 and have got rectal bleeding, you pretty much go to the front of the queue because they’ll think it’s rectal cancer. If you’re 35 and have rectal bleeding, they’ll say ‘It’s haemorrhoids, go away’.”

What treatments are available in New Zealand?

Treatment depends on the stage and site of the cancer. Early-stage cancers can be removed via a colonoscopy or excised via the rectum.

“If it’s a bit bigger, it involves surgery to resect the tumour. And if it’s a bit more advanced than that, then you may need chemotherapy as well. If it’s in your rectum and it’s a locally advanced tumour, you’ll get radiation and chemotherapy prior to surgery.”

Bethany Reitsma is a lifestyle writer who has been with the NZ Herald since 2019. She specialises in all things health and wellbeing and is passionate about telling Kiwis’ real-life stories.