Danni Duncan colon cancer symptoms, dismissed for months as irritable bowel syndrome, were eventually traced to a stage 2B tumour discovered during a colonoscopy in May 2025, when Duncan was 39. Her case is one of a growing number among younger Australians, as early-onset bowel cancer incidence has risen 65 per cent since 2005, according to Cancer Council Victoria.
Duncan, who lives on the Gold Coast, had struggled with IBS since childhood. She recalls being on her hands and knees in pain as early as age five or six, and was formally diagnosed with IBS at around 11. Elimination diets through primary school and, later, a shift to whole foods and marathon training as an adult brought her symptoms under control. She became a fitness and nutrition coach, and by her late 30s considered herself in peak health.
Then the bowel changes returned. She attributed them to IBS and began taking Metamucil, a fibre laxative, to manage constipation. Persistent bloating followed the birth of her fourth child in September 2024. At around 20 weeks pregnant, her iron levels had dropped to their lowest ever. Even after an iron infusion they did not recover, though her doctor attributed the deficit to pregnancy and recommended supplements.
Warning signs that went unread
By early 2025, around five months after giving birth, Duncan began training for a marathon scheduled for March. Her performance deteriorated in ways she could not explain: breathlessness, an inability to lift her pace, and dizzy spells in the gym. She dropped out of the race when she was three-quarters of the way through. A month after that, in April 2025, she nearly fainted one morning and made it to her couch.
A blood test that day showed a haemoglobin level of 70 g/L, against a normal range of 120 to 160 g/L for adult women, indicating severe anaemia. A colonoscopy two weeks later confirmed a tumour in her colon. Less than two weeks after that, she underwent surgery including a right hemicolectomy, with 17 lymph nodes also removed. Cancer was found in the lymph node channels but not the nodes themselves, placing her at stage 2B and at elevated risk of recurrence.
Her doctor recommended four rounds of chemotherapy to reduce that risk. The treatment brought cold sensitivity from oxaliplatin, her chemo medication. ‘Everything seizes up,’ Duncan said. ‘Your throat seizes up, you can’t breathe; your face seizes up like you’re having a stroke.’ She wore gloves to open her fridge or handle weights. The hardest part, she said, was having to stop breastfeeding: chemo drugs can pass to a baby through breast milk, and her daughter was only seven months old when the diagnosis came. ‘It’s broken my heart and it still breaks my heart,’ she said.
As of November 2025, her CT scans and colonoscopy showed no signs of cancer. She now faces three more monthly blood tests, with yearly CT scans and colonoscopies every two years thereafter.
Danni Duncan colon cancer and the broader early-onset surge
Her experience reflects a pattern documented by Bowel Cancer Australia: more than 1,800 young Australians are diagnosed with early-onset bowel cancer each year, and younger patients may spend between three months and five years seeing multiple doctors before receiving a diagnosis, making ten or more GP visits along the way. Time to diagnosis can be up to 60 per cent longer for younger people than for older patients, in part because bowel cancer remains associated in clinical practice with older age groups.
Cancer Council Victoria notes that bowel cancer is now the most common cancer in young men and the third most common in young women, behind breast and thyroid cancers. That shift in the epidemiology makes cases like Duncan’s both more common and more likely to be delayed, because the presenting symptoms, changes in bowel habit, bloating, and fatigue, are readily attributed to conditions such as IBS.
Duncan, whose 37-year-old friend died from colon cancer the year before her own diagnosis, said the moment of her own diagnosis brought immediate thoughts of her children. ‘That thought broke me,’ she said, ‘and then my mind just switched to, “I have to fight this because I have children.”‘
She is now training for the New York City Marathon, a race she had planned to run in 2025 but postponed due to treatment. She will run it with her husband in support of the Jodi Lee Foundation, a colon cancer organisation in Australia. Her message to anyone with persistent or unusual bowel symptoms is direct: ‘Stand up for yourself. Be like, “I’m not too young.” If you’ve got symptoms, push, find another doctor.’
The original story was reported by Business Insider.