If there is one thing that Australians aged 45 years or older should do, it is to collect a fecal sample, according to Eleonora Feletto, PhD, associate professor of medicine and health at the University of Sydney.

“It can be off-putting to do, and it is a weekend event because we are one of only a few countries in the world that require two samples across different days,” Feletto, who is also a principal research fellow and cancer epidemiologist at the university, told Medscape News Australia. “But what we have known for ages is that once you do it, there’s an 80% chance you will do it again.”

Bowel cancer, also known as colorectal cancer, develops when cells in any part of the large intestine grow in an uncontrolled way. In 2025, it was the fifth most commonly diagnosed cancer in Australia, with an estimated 14,784 new cases diagnosed, according to government data. Bowel cancer is also the second most common cause of cancer-related deaths, with 5235 estimated deaths last year.

However, since 2000, incidence rates have decreased more for bowel cancer than for any other cancer. But the good news comes with a warning: Bowel cancer incidence has increased in those younger than 50 years since mid-2000. Additional research has found that early-onset cancer incidence rose by 5%-9% every year between 1990 and 2020.

Today, 1 in 8 Australians diagnosed with bowel cancer is younger than 50 years.

Biologic and Behavioral Differences

What is going on? In short, no one has a definitive answer, Savio Barreto, MBBS, PhD, professor of surgery at Flinders University in Adelaide, told Medscape News Australia. Barreto, who also is a gastrointestinal, hepatic-pancreatic-biliary, and liver transplant surgeon, has researched early-life influences on cancer and suspects that the cumulative effect of multiple exposures and stresses can overwhelm the body’s protective systems, triggering epigenetic modifications.

“We now know that epigenetic modifications can influence every hallmark of cancer,” he said. “Stressors are smoking, alcohol, obesity, illicit drug use, and so on. But the list of such stressors is growing and may include microplastics. I think there is a component of increased susceptibility, too, in recent years. The rise in metabolic syndrome, for example, could play a role.”

Other research has looked into the potential role of Escherichia coli infection in childhood and the role of an altered gut microbiome.

One of Australia’s largest real-world studies of younger adults with advanced bowel cancer, published last month and led by Barreto, confirmed the long-held belief that early-onset cancers differ from late-onset disease in biology and behavior. It analyzed data from almost 1700 Australians whose bowel cancer had spread only to the liver and found that younger patients differed from older patients in tumor biology, disease characteristics, and survival outcomes.

For Barreto, understanding how the disease presents and progresses in younger cohorts is critical and could help doctors better tailor treatments. “We hope the findings of the study will further inform decision-making based on the location of the primary cancer, as well as the timing of presentation of the liver metastases,” he added.

Encouraging Participation in Screening

Australia was one of the first countries to implement a national bowel cancer screening program in 2006. Every 2 years, a kit is sent via email to adults aged 50-74 years. It detects microscopic amounts of blood that may indicate the presence of cancer or a precancerous lesion, leading to earlier detection and higher rates of survival. The decreasing rates of bowel cancer in adults older than 50 years may indicate that the program works.

But it also requires greater participation because, as experts told Medscape News Australia, the current 40% participation rate is less than optimal. In 2024, eligibility for the program was expanded, enabling those aged 45-49 years to request a kit.

“For us, this is a real opportunity to screen the next most vulnerable group,” said Feletto, whose research helped inform the updated screening program. “The test can catch it early so that it never develops into cancer. We are so lucky in Australia to have such a program.” 

General practitioners (GPs) can play a vital role in getting more patients enrolled in the program, Jon Emery, MB BCh, DPhil, professor of family medicine at Nanyang Technological University in Singapore, told Medscape News Australia. Emery also is the director of the Research Institute for Cancer Prevention, Screening and Early Detection.

“GPs could be more systematic in offering the kit to patients in the 45-49 age group through the alternative access pathway. Ideally, the program should have the same process of invitation for people aged 45-49 years as exists with age 50 years and above, with specific campaigns to raise awareness in younger people to encourage them to start screening,” he said.

The alternative access pathway allows registered healthcare providers to bulk order and provide free test kits to eligible patients during consultations. Feletto has been working with GPs on this initiative. “In the past, GPs haven’t been directly involved in the program. If a patient came in, they would ask them to register and get a kit sent in the email,” she said.

“Quite often, GPs were issuing a private pathology for a referral to a blood test, urine test, and a stool test through the Medicare Benefits Schedule (MBS), but that’s not part of the program. Now GPs themselves, once they are registered in the portal, can bulk order the kits and have them there ready to give out. They’re more involved now.”

The health check at ages 45-49 years, which is billable to MBS, is a wonderful opportunity for cancer screening, said Feletto. “There are electronic prompts that will let the GP know if someone is underscreened or has never been screened. It’s an opportunity to engage the patient,” she said. “But we must remember that GPs are overwhelmingly overloaded. We are asking GPs to do a lot in terms of disease management and prevention. We have to be really thoughtful about what we’re saying.”

The Challenges Facing GPs

Younger patients present to their GPs with possible symptoms of bowel cancer that sometimes go unrecognized. Studies indicate that younger patients may spend between 3 months and 5 years consulting multiple doctors before they receive a bowel cancer diagnosis. They may make 10 or more visits to the GP. In several studies, patients attributed their GPs’ low suspicion of cancer to their young age, which influenced the investigations and referrals and ultimately delayed diagnosis.

It’s important to remember that while incidence in patients younger than 50 years is increasing, risk ultimately increases with age, said Emery. “Even though there is an increased incidence of colorectal cancer in under-fifties, your risk that a particular symptom, such as change in bowel habit or abdominal pain, is due to cancer is greater in older patients.

“The challenge for GPs is that symptoms of colorectal cancer are common, and most are due to benign conditions, especially in younger people. In public health systems, there are long waiting times for colonoscopy, and GPs need to select which patients are more likely to have colorectal cancer and warrant referral for colonoscopy and which can be monitored in primary care to see if symptoms settle or progress.”

GPs can order several simple tests to help this triage, Emery added. They include a full blood count and inflammatory markers, which can show early signals in patients with cancer.

Patients with symptoms, but without other features that suggest immediate referral, need special attention. “This means providing patients with a planned timeframe for follow-up and review of their symptoms, and they need to return sooner if new symptoms develop,” said Emery.

Feletto led projects that developed resources and referral tools for health professionals to improve colonoscopy access for patients who need it. “Our problem in Australia is that colonoscopy is resource-intensive, and wait times are substantial,” she said. “If we can reduce the number of people who are going for colonoscopy who could be triaged in a different way, then it would ease the burden on the health system and open up colonoscopy for those who really need it.”

Feletto, Barreto, and Emery reported having no relevant financial relationships.