Background: Colorectal cancer is the third most common cancer among both men and women in the United States. A colorectal cancer begins when normal cells in the lining of the colon or rectum change and grows uncontrollably, forming a mass called a tumor. Case presentation: A 54-year-old woman complained of epigastric pain for the last four months and the pain increased in severity in the last few days. Computed tomography (CT) scan showed mid transverse colon tumor with the absence of pericolic fat streakiness, lymphodenopathy and liver metastases. The patient has diabetes mellitus (DM) type 2 and hypertension. She has been on insulin therapy for years (subcutaneous (S/C) Actrapid 30 u TDS and S/C Insulatard 8 u ON). Patient is obese with BMI of 36.5 kg/m2. The colonoscopy and pathological examination showed polypoidal tumour (Transverse) with length of 5.5 cm, the lumen of the colon is almost completely obstructed by the tumour. The patient underwent right hemicolectomy and her condition improved afterwards. Conclusion: Diabetes Mellitus and aggressive insulin therapy may be the underlying factors that causing emergence of colon cancer in current patient, even though there is no family history for cancer.