Diagnosing colorectal cancer

Whenever colon cancer is diagnosed, an assessment of how much it has spread should include an abdominal CT scan and a plain film chest X-ray. If the diagnosis is for rectal cancer, then a pelvic MRI scan is required as part of a locoregional assessment and a chest/abdominal CAT scan to study any distant metastasis. If the CAT scan reveals small hepatic lymph nodes suspected of metastasis, a liver MRI may help characterise and determine the number of lesions. 

Regarding tumour markers, lactate dehydrogenase (LDH) and carcinoembryonic antigen (CEA) concentrations in blood must be determined once the diagnosis of colorectal cancer has been confirmed and before starting any treatment. The latter marker provides valuable prognostic information and is very useful throughout patient follow-up as high levels of CEA after cancer resection can be a sign of recurrence. However, it is important to emphasise that the CEA test cannot be used in either the diagnosis or screening of colorectal cancer.