Late last year, I met my new 64 year-old clinic patient who just moved into town. During a brief discussion about preventive health, I asked her when she had her last colonoscopy for colon cancer screening. She emphatically responded: “Never. I will probably be dead in 10 years anyway [from an unrelated cause]“. Her view on life may have been surprising, but her reluctance to obtain a colonoscopy wasn’t. Who could blame her? The prospect of having a scope inserted into the rectum and advanced through the colon is not appealing. Fortunately, there are alternate modalities for colon cancer screening, two of which (stool DNA and virtual colonoscopy) have just been added to official guidelines.

A consortium of specialty organizations (American Cancer Society, US Multi-Society Task Force on Colorectal Cancer, and American College of Radiology) recently published in CA: A Cancer Journal for Clinicians¹ the first consensus guidelines for colorectal cancer (CRC) screening. The guidelines are designed for asymptomatic average-risk adults over the age of 50; these criteria exclude individuals with a personal or family history of CRC, adenomas, inflammatory bowel disease (IBD), or other genetic risk factors.

The tests that primarily detect colorectal cancer:

• high-sensitivity guaiac-based fecal occult blood test (gFOBT) every year;
• high-sensitivity fecal immunochemical test (FIT) every year; or
• stool DNA test (sDNA) every [interval not yet established]

The tests to detect adenomatous polyps and colorectal cancer:

• flexible sigmoidoscopy (FSIG) every 5 years;
• colonoscopy every 10 years;
• double contrast barium enema (DCBE) every 5 years; or
• CT colonography (CTC) every 5 years.

Advances in molecular genomics have paved the way for genetic-based CRC surveillance. Clinical laboratory analysis of stool DNA (sDNA) permits detection of mutations associated with the progression of colonic adenomas and carcinomas. Despite ease of sample collection and analysis, the test has a sensitivity that ranges from 52% to 91% (specificity 93% to 97%). The traditional fecal occult blood tests (FOBT) are much simpler to process (smear the stool on the card, apply solution, and view results in a minute) and can be done anywhere (in clinic or at home), but have lower sensitivities. Fecal immunofluorescence (FIT) has an intermediate sensitivity for colorectal cancers, shown in one study to be around 82%².

CT colonography (CTC) a.k.a. “virtual colonoscopy” has been under development and in the news since the 1990’s, but has only recently been validated as a screening tool. Although many clinic patients may be hesitant to undergo traditional colonoscopies, CTC will probably gain wider acceptance by the public. CTC is essentially a CT scan of the abdomen with higher resolution and 3D reconstruction. This method does not require sedation or ingestion of a cathartic. Similar to traditional colonoscopies, however, there is still need for bowel insufflation with room air or carbon dioxide. A drawback is that if a suspicious polyp is detected, the patient would not be adequately prepped for the traditional colonoscopy required for polyp removal.

Colorectal cancers constitute the third most common type of cancer and second leading cause of cancer-related death. Annually, there are 150,000 new cases diagnosed in the United States and 50,000 deaths. As this is one of the few preventable cancers through early detection and intervention, good surveillance screening is an important public health measure. Although sDNA screening does not provide added convenience to previous screening modalities, it adds to the array of options. The advent of CT colonography is, however, more notable. Unlike the stool-based tests, this screening measure can be used for detection of CRC and pre-cancerous adenomas. It also avoids some of the unpleasant features of traditional colonoscopies, such as colon preparation, sedation, and insertion of a scope via the rectum. The latter reason alone will hopefully address some excuses of the many patients who otherwise would have balked at colon cancer preventive screening.

• Sources:
• 1. Levin B, Lieberman DA, McFarland B, et al. Screening and surveillance for the early detection of colorectal cancer and adenomatous polyps, 2008: a joint guideline from the American Cancer Society, the US Multi-Society Task Force on Colorectal Cancer, and the American College of Radiology. CA Cancer J Clin 2008 [Epub ahead of print].
• 1. Allison JE, Sakoda LC, Levin TR, et al. Screening for colorectal neoplasms with new fecal occult blood tests: update on performance characteristics. J Natl Cancer Inst 2007;99:1462–70.