Fecal Immunochemical Testing Effective in Screening for Colon Cancer but Not Polyps

A recent review of multiple studies has concluded what was suspected all along: Fecal Immunochemical Testing (FIT) is an accurate non-invasive test to screen for colon cancer but is not as good at detecting precancerous polyps.

Most cases of colon cancer begin with the development of benign colon polyps, growths that protrude into the intestinal cavity. While most do not cause health problems, some can become cancerous and potentially spread to other parts of the body (metastasize).

Screening is the process of looking for a disease in people without any symptoms. For colon cancer, there are a few ways to do this. There are invasive tests like flexible sigmoidoscopy and colonoscopy, which require patients to prepare by following a special diet or clear out their intestines with enemas or strong laxatives—after which their doctor will insert a tube with a camera at the end into their rectum to look for any abnormal areas in their colon and rectum, while under sedation. If polyps are found, they can be removed, reducing the risk of cancer. There are also less commonly performed radiology tests like double contrast barium enemaand CT colonography.

However, non-invasive tests like FIT allow patients to collect a stool sample in their own bathroom without special preparation. The sample is placed on a card or in a tube, which is then brought or mailed to their doctor's office or a laboratory. There are no dietary restrictions as with colonoscopy, and FIT detects human hemoglobin (blood) protein, which can be a sign of cancer. FIT needs to be done annually, which is more frequent than other tests like colonoscopy. If FIT is positive, a follow-up colonoscopy is done, and it is only on colonoscopy or flexible sigmoidoscopy that cancers can be biopsied or polyps removed and sent for microscopic examination.

The researchers reviewed 12 studies to determine how well FIT worked for detecting colorectal cancer. They found that while FIT correctly identified 93 out of 100 cancers (93% sensitivity), it was positive only about half of the time (48% sensitivity) in people with high-risk polyps that can develop into cancer, namely "adenomatous" polyps 1 cm or greater in size, or those with 25% or more of a villous (finger-like) microscopic architecture, or harboring high-grade dysplasia (complex glands and atypical cells).

While FIT falls short in not being able to pick up polyps, it is recommended by major health organizations as a screening option for people at average risk for colon cancer. For people who are at intermediate or high risk of colorectal cancer (e.g., family or personal history), a colonoscopy is usually recommended. However, with additional research that includes rigorous studies with many more participants, FIT may become a means to "promote more individualized and more flexible alternative screening options in patients at higher risk of CRC [colorectal cancer] based on their own values and preferences," say the researchers.