Colorectal Cancer Screening Modalities

Imaging Techniques

Colonoscopy

A colonoscopy involves inserting a flexible, thin, lighted tube with a camera (colonoscope) into the rectum to visualize the entire colon. Biopsies can be taken during the procedure to examine suspicious tissue. This is considered the gold standard for colorectal cancer screening due to its high sensitivity and ability to detect and remove precancerous polyps.

Virtual Colonoscopy (CT Colonography)

A non-invasive imaging technique using computed tomography (CT) scans to create detailed three-dimensional images of the colon. Requires bowel preparation. While less invasive than a colonoscopy, it may miss smaller polyps and requires a follow-up colonoscopy if suspicious findings are detected.

Sigmoidoscopy

Similar to a colonoscopy, but only examines the sigmoid colon and rectum, the lower part of the large intestine. Less comprehensive than a colonoscopy, but still useful in detecting polyps and cancers in this region. Flexible sigmoidoscopy is more common than rigid sigmoidoscopy.

Stool-Based Tests

Fecal Occult Blood Test (FOBT)

Detects microscopic amounts of blood in the stool, which may indicate the presence of a polyp or colorectal cancer. Several types exist, including guaiac-based and immunochemical tests. Sensitivity is lower than colonoscopy, requiring repeated testing.

Fecal Immunochemical Test (FIT)

A more sensitive and specific type of FOBT that detects human blood proteins in the stool. Generally preferred over guaiac-based FOBT.

Stool DNA Test

Analyzes DNA in a stool sample to detect abnormal cells or genetic markers associated with colorectal cancer. This is a non-invasive option, but may have limitations in sensitivity and specificity compared to colonoscopy.

Other Screening Methods

Capsule Endoscopy

A less commonly used technique involving swallowing a small camera capsule that transmits images as it passes through the digestive tract. Primarily used for evaluating small bowel disorders, not usually for routine colorectal cancer screening.

Factors Influencing Choice of Screening

The selection of an appropriate screening method depends on several factors, including age, family history of colorectal cancer, personal risk factors, and individual preferences. Guidelines from professional medical organizations offer recommendations for screening intervals and appropriate tests based on these factors.