The efficacy of additional metformin to aspirin for human rectal aberrant crypt foci: double-blinded randomized controlled trial

INTERVENTION: aspirin metformin medication CONDITION: Colorectal adenoma, carcinoma in situ ; Colorectal Neoplasm Colorectal Neoplasm PRIMARY OUTCOME: The amount of change rectal ACF in aspirin plus placebo group and aspirin plus metformin group after 8weeks intervention SECONDARY OUTCOME: The number of rectal ACF before and after intervention in both group ; Ki67 labeling index of colorectal adenoma/cancer and normal mucosa before and after intervention ; Safety INCLUSION CRITERIA: Patients both with rectal ACF and resectable polyps