The rising incidence of young-onset colorectal cancer may be explained by type 2 diabetes (T2D) being a potential risk factor, a study from South Australia suggests.
T2D was found to be four times more common in people who developed colorectal cancer below the age of 55 than in an aged-matched control group of people without colorectal cancer, according to researchers from the University of Adelaide.
In a review of a cohort of ninety patients from the South Australian Young Onset (SAYO) colorectal cancer study, a history of T2D was confirmed in 17 (19%) patients compared with 12 of 240, (5%) of a control group of people who had undergone colonoscopy with clear results (P < 0.001; odds ratio = 4.4; 95% confidence interval, 2.0–9.7).
In the study, published in the Asia-Pacific Journal of Clinical Oncology, the median age of young-onset colorectal cancer patients was 44 years (18–54), which was similar to that of controls.
Left-sided (distal) cancers accounted for 75% of cases overall, with lower rates (64%) in females than in males (88% ).
Colorectal cancer-related pathogenic germline variants were found in 12% of patients with young onset cancers, and a similar proportion reported a family history of colorectal cancer, but there was overlap in only one case.
No pathogenic variants in familial diabetes-associated genes were seen.
The study investigators said 90% of young onset colorectal cancers could not be explained by genetic factors and it had previously been thought that lifestyle factors such as diet might explain the rising incidence.
However they noted that recent studies had not found any evidence of an association between obesity per se and young onset colorectal cancer.
The strong association between T2D and colorectal cancer may be associated with a proinflammatory milieu involving insulin-dependent growth factors at a molecular level, they suggested, but could also be related to an altered microbiome.
“Though the mechanism remains unclear, our observations suggest that there is enrichment for personal history of T2D in YOCRC patients,” they wrote.
“A diagnosis ofT2D could therefore potentially identify a subset of young adults at increased risk for CRC and in whom early screening might be appropriate.”
And with around 1300 Australians under 50 years diagnosed with colorectal cancer annually, they suggested that the current bowel cancer screening program might be extended to people over 40 if there is a personal history of T2D.
“Faecal immunochemical tests (FIT) should be considered for screening these increased risk patients, especially as their cancers tend to be in the distal colon (for which the FIT is more sensitive),” they wrote.