From the Guidelines
For a patient looking for colon cancer, the best imaging order is to start with a total colonoscopy for diagnostic confirmation and to rule out synchronous tumors, as recommended by the most recent guidelines 1. This approach allows for direct visualization of the entire colon and immediate removal of precancerous polyps.
- If a total colonoscopy is not possible, combining a limited left-sided colonoscopy with CT colonoscopy is an alternative 1.
- For patients with suspected advanced disease or metastasis, a CT scan of the thoracic, abdominal, and pelvic cavities with i.v. contrast administration is the preferred radiological method for evaluating the extent of colon cancer 1.
- Additionally, contrast-enhanced MRI can be used to evaluate the relationship of locally advanced tumors with surrounding structures or to define ambiguous liver lesions 1. Some studies also support the use of CT colonography in local staging of colon cancer, with a staging accuracy of 81% and a sensitivity of 93% for detecting polyps > 1 cm 1. However, the most recent and highest quality study recommends total colonoscopy as the first line of imaging for colon cancer diagnosis 1.
- The use of CT colonography, MRI, and other imaging modalities may be considered in specific situations, such as incomplete colonoscopy or suspected advanced disease, but total colonoscopy remains the gold standard 1.
From the Research
Imaging Options for Colon Cancer Screening
The following are some imaging options for colon cancer screening:
- Colonoscopy: considered the gold standard for detection of colorectal precancerous lesions 2
- CT colonography (virtual colonoscopy): a minimally invasive method for CRC screening and diagnosis 3, 4, 5
- Flexible sigmoidoscopy: a screening strategy recommended by the US Preventive Services Task Force 6
Recommended Screening Strategies
The US Preventive Services Task Force recommends screening with one of several strategies, including:
- High-sensitivity guaiac fecal occult blood test (HSgFOBT)
- Fecal immunochemical test (FIT)
- Multi-target stool DNA (mt-sDNA) test
- Computed tomographic (CT) colonography (virtual colonoscopy)
- Flexible sigmoidoscopy
- Flexible sigmoidoscopy with FIT
- Traditional colonoscopy 6
Factors to Consider When Choosing a Screening Test
When choosing a screening test, factors to consider include:
- Invasiveness of the test
- Test performance
- Screening interval
- Accessibility
- Cost 6
Emerging and Novel Screening Modalities
There are several emerging and novel CRC screening modalities that are not yet approved for first-line screening in average-risk individuals, including:
- Blood-based screening or "liquid biopsy"
- Colon capsule endoscopy
- Urinary metabolomics
- Stool-based microbiome testing for the detection of colorectal polyps and/or CRC 6