Background: An in-patient presented with atypical primary liver mass and was suspected of having liver metastasis. One method of investigation is colonoscopy; however, there are currently no clear guidelines to indicate when this procedure should be performed.
Material and Method: This was a retrospective review of 6 years’ data from the surgical endoscopic unit in Rajavithi Hospital. The inclusion criteria were: (1) patient presented with liver mass, (2) radiological findings (mainly from CT scan or MRI) were not typical for hepatocellular carcinoma (HCC), intrahepatic cholagiocarcinoma (ICGC) and other primary liver tumors. The exclusion criteria were: (1) patients did not undergo the operation in Rajavithi Hospital, (2) there was loss of patient data during the follow-up period.
Result: A total of 1,532 cases underwent colonoscopy, of which 109 met the inclusion criteria. There were 24 cases of positive primary colorectal cancer and the incidence was 22% (95% CI 14.1 29.9), and 1 case of terminal ileum cancer. The final results after operation showed 40 cases of HCC, and 21 cases of intrahepatic cholangiocarcinma. Risk factors for testing positive for colorectal cancer were: presenting with GI symptoms; abnormal CEA levels; and positive family history of colorectal cancer.
Conclusion: To increase the incidence of positive results for colorectal cancer and reduce unnecessary colonoscopy in patients who present with liver mass, the factors which indicate colonoscopy should be patients who present with GI symptom, abnormal CEA level, and whose family history raises concern.

Keywords: Colonoscopy, Primary colorectal cancer, Liver mass, Incidence