University of Otago (Christchurch) researchers found colorectal cancer rates (CRC) in older age groups had decreased — possibly in part due to older New Zealanders taking part in bowel cancer screening.
But rates of early onset colorectal cancer (EOCRC) have increased by 26% per decade on average, over the past 20 years.
Of the 56,761 cases of CRC diagnosed in New Zealand between 2000 and 2020, more than 3700 were early onset, and 44% of all EOCRC cases occurred in the 45-49 year age group.
By comparison, there was an 18% decrease per decade in those aged 50-79 over the same time frame.
Data modelling showed if these trends continued to 2040, there would be 524 cases of early onset colorectal cancer diagnosed per year in New Zealand — an increase of 255 cases per year when compared with numbers seen in 2020.
Lead author, University of Otago surgical trainee and PhD candidate Dr Oliver Waddell said of particular concern was the CRC rates in Māori were increasing disproportionately to the overall population, and was being driven by more younger Māori patients.
While overall incidence of CRC remains lower in Māori compared to the total population, incidence rates of colorectal cancer in Māori under 50 years rose by 36% per decade on average, and accounted for 18% of all cases diagnosed in 2020.
"This is of grave concern, because once they are diagnosed with colorectal cancer, Māori are more likely to die from their disease than non-Māori, and also more likely to be diagnosed with stage 4 advanced disease, possibly due to delayed diagnosis and inequitable access to cancer treatment.
"If these increases go on unchecked, we will see colorectal cancer rates in Māori overtake those of the general population."
The study authors are now calling for the bowel cancer screening age (60 for non-Māori and 50 for Māori), to start at at least 45, to help combat inequity.
"Unfortunately, in over a third of patients diagnosed with a bowel cancer under the age of 50, by the time symptoms have developed, the cancer has already spread to stage 4 disease, so we need to find these cancers earlier before it’s too late for a cure," he said.
"In the long term, it will save the New Zealand health system money from reduced treatment costs due to earlier diagnosis, not to mention the lives that will be saved."
The authors said more research was needed to establish why rates were rising so dramatically, both here and overseas.
While conventional risk factors for bowel cancer are known (such as obesity, alcohol, processed meat, sugary drinks and a high-fat, low-fibre diet), they say the microbiome in EOCRC patients differs — possibly reflecting the impact of early life events or environmental factors such a Caesarean delivery, formula feeding, antibiotic use, changing diet, synthetic food dyes, MSG high fructose corn syrup, or microplastics.
Bowel cancer remains the second-highest cause of cancer death in New Zealand, with more than 1200 people dying each year.
