Context Hyperinsulinemia is associated with colon carcinoma in the general population. Patients with acromegaly are considered to be at risk to develop colonic lesions and typically have hyperinsulinemia.

Objective To evaluate the role of fasting insulin levels on the prevalence of colonic adenomatous polyps or adenocarcinoma in acromegaly.

Design Analytical, observational, prospective study.

Patients 210 patients (111 women, age 20–82 yrs) undergoing complete colonoscopy at diagnosis of acromegaly.

Results Colonic lesions were found in 81 patients (38.6%) and consisted of hyperplastic polyps in 33 (15.7%), adenomatous polyps in 42 (20.0%), and adenocarcinoma in 6 patients (2.8%). Polyps were single in 22 cases (27.1%). Fasting insulin levels were significantly lower in patients without lesions (16.0±7.5 mU/liter) than in patients with hyperplastic polyps (22.4±8.8 mU/liter, p<0.01), adenomatous polyps (38.0±15.9 mU/liter, p<0.0001) and adenocarcinoma (59.0±30.6 mU/liter, p<0.0001). Fasting insulin levels were also lower in patients with hyperplastic polyps than in those with adenomatous polyps (p<0.01). The odds ratio for harbouring colonic adenomas was 14.8 (95% CI=4.4–51.2, p<0.0001) and 8.6 times higher (95% CI=2.8–29.0, p<0.0001) in patients with fasting insulin levels in the upper tertile [27.1 mUI/liter (n=28)] compared to the lower tertile [12.1 mUI/liter (n=40)] and middle tertile [>12.1-<27.1 mUI/liter (n=74)], respectively.

Conclusion An increase in fasting insulin levels is associated with an 8.6- to 14.8-fold increased risk of presenting with colonic adenomas in acromegaly.