Which of the following is NOT listed as a common colorectal cancer screening modality by USPSTF guidelines?

• A. Colonoscopy
• B. Flexible sigmoidoscopy
• C. CT colonography
• D. Stool-based tests

Answer: (C)

Start with what the USPSTF considers as widely used colorectal cancer screening options. Colonoscopy and flexible sigmoidoscopy are primary endoscopic methods, and stool-based tests (such as fecal tests and stool DNA tests) are noninvasive options that are regularly recommended. CT colonography, while listed as an option in some USPSTF guidance, is not categorized as a common modality in the sense of being a standard, widely adopted screening method. This reflects practical considerations: CT colonography does not allow immediate biopsy or polypectomy, requires a follow-up colonoscopy if findings are positive, involves radiation exposure, and has variable availability and coverage across settings. Because of these limitations, it isn’t grouped with the main, commonly used modalities in USPSTF recommendations, making it the best choice for not being listed as a common modality.