Objective: Some studies have found that people with type 2 diabetes mellitus are at increased risk of neoplasms, especially colorectal cancer (CRC). In other studies it is also suggested that there is a higher incidence of diabetes mellitus in patients with CRC. The aims of this study were to assess whether the incidence of type 2 diabetes mellitus and impaired glucose tolerance (IGT) are higher in subjects with CRC and to determine the difference between diabetic subjects and healthy controls regarding glucose metabolism (glycaemia, insulinaemia, serum levels of C-peptide) as well as insulin resistance and sensitivity.
Material and methods: The study included a total of 80 subjects: 40 enrolled patients (20 M, 20 F) with newly diagnosed sporadic colorectal cancer and 40 subjects with endoscopically excluded CRC or adenomas serving as controls. Subjects were matched for gender, age and body mass index (BMI) (age +/- 5 years BMI +/- 1 kg/m2). A 75-g oral glucose tolerance test was performed after an overnight fast. Samples for glycaemia, serum levels of C-peptide and insulin were taken at 0, 30, 60, 90, 120 and 150 min of the study. HOMA-IR, EIR, EIR/HOMA-IR indexes were calculated.
Results: There was a significantly higher incidence of impaired glucose metabolism (IGM-diabetes mellitus or IGT) in CRC subjects. No differences were found in levels of glucose, insulin or C-peptide. Insulinaemia and C-peptide curves showed a shift typical of diabetes, in the form of a delayed insulin release peak. The HOMA-IR, EIR as well as the EIR/HOMA-IR indexes showed no differences between groups.
Conclusions: A significantly higher incidence of IGM appears to occur in CRC patients than in the healthy population. This phenomenon is not dependent on age and body-weight, which may suggest that it is cancer that predisposes to diabetes rather than the other way round. The neoplastic process in the colon is not associated with hyperinsulinaemia or insulin resistance, but in CRC patients, pancreatic B-cell dysfunction typical of the early stages of diabetes is seen.