CT Colonography or Bust
Is CT colonography the future of colorectal cancer screening or is it a sinking ship?
Now that I can count the months until I am colorectal cancer screening–eligible on my two hands (great, just great ), the latest installment of the Radiology Firing Line podcast series made me sit up straight up and pay close attention. Listen as RFL host Saurabh (Harry) Jha, MBBS, interviews his University of Pennsylvania colleague, abdominal imager Hanna Zafar, MD, about CT colonography (CTC), also called virtual colonoscopy:
Screening with optical colonoscopy is recommended every ten years between the ages of 50 and 75. If each screening came back negative, this would mean only two or three exams over a lifetime for most people, making optical colonoscopy the lowest-frequency screening study. With optical colonoscopy, diagnostic follow-up of positive results, such as polypectomy or biopsy, can be immediate, at the time of screening. On the opposite end of the frequency spectrum are annual fecal immunochemical test or hs-gFOBT (high-sensitivity guaiac-based fecal occult blood test) stool tests. These are less sensitive and less specific than OC, but relatively inexpensive. There's no time off work (the specimen is collected at home), no bowel prep, no sedation, no scope or rectal tube insertion, no air insufflation, no sedation, no risk of bowel injury, no ionizing radiation, and no CT incidental findings. Compared to hs-gFOBT, fecal immunochemical test produces fewer of the screening false positives that result in follow-up OC.
A middle ground between optical colonoscopy and annual stool tests is flexible sigmoidoscopy every five years combined with an annual fecal immunochemical test every year. Optical colonoscopy evaluates the entire colon and is more sensitive, but flexible sigmoidoscopy has fewer complications and does not require sedation or extensive bowel prep. Another study is mid-way in frequency between screening optical colonoscopy and stool tests is CTC every five years. The ACS and ACG already include CTC as an option for colorectal cancer screening. The USPSTF currently does not, but the task force is continuing to accumulate evidence that may change future recommendations. Currently, the USPSTF gives CTC a grade of "I," which refers to insufficient evidence to assess the procedure's benefits and harms. Assuming diagnostic optical colonoscopy follow-up for CTC-identified lesions measuring ≥6 mm, CTC "could potentially yield approximately the same number of life-years gained, with a similar balance of benefits and harms" as optical colonoscopy, according to a systematic review performed for the USPSTF, which may positively impact the next round of recommendations. You can compare current final and on-going draft USPSTF recommendations.
The individual patient decision to undergo screening and the choice of screening test is not simply a matter of what technology is more accurate, has a better risk-to-benefit profile, or is more convenient and comfortable. "Full endorsement and reimbursement for [CTC] by the USPSTF and CMS are absent, so this screening option is infrequently used," wrote the authors of a recent JACR article. For many patients, cost is a critical factor in deciding whether or not to proceed with screening. If the procedure is not covered by insurance, many people won't get screened.
We're all familiar with the following facts about colorectal cancer: second most common cancer diagnosed in the U.S. (over 140,000 diagnoses annually), third leading cause of U.S. cancer death (50,000 die due to late detection), 90 percent cure rate with early detection, less than half of eligible adults undergo recommended screening. We can do better, so much better. Because the simple fact is that, as researchers point out, "any screening strategy is more cost effective compared with no CRC screening, and high-quality evidence supports this recommendation."
The ACR has strongly urged the USPSTF to recognize CTC as a recommended test for CRC screening . In a released statement supporting the CT Colonography Screening for Colorectal Cancer Act of 2016 (H.R. 4632/S. 2262) , the ACR states, CTC is equally as effective as OC and that a "contributing factor to poor patient screening rates may be the invasiveness of...colonoscopies." Leaving aside equivalent effectiveness, technological advantages, lower risks, comfort advantages, and cost savings of CTC for a minute, I can think of at least one more compelling reason CTC should be a covered service: equal access to screening. Can the people who need to be screened get easy access to these procedures? There is no point in recommending the gold-standard screening colonoscopy if you don't offer it in a way that people can readily access and afford.
I work in a largely rural state that is peppered with very small critical-access hospitals. If there are personnel sufficiently trained and qualified to perform rectal tube insertion and air insufflation, CTC could be offered in these small hospitals (which do have CT scanners). The acquired image data could be networked to a remote centralized center for post-processing, with interpretation performed by specialty abdominal imagers. Local access to CTC for appropriate candidates who might otherwise go without screening would be less disruptive (especially for farmers, who can take very little time off) if no gastroenterologist serves the region. In a time of greater interconnectivity, people should not be denied basic recommended screening services based on their geographic distance from specialists. CTC can close this important screening gap.
As for me, when the time comes, what option will I choose? I am actually undecided at this time, but CTC is probably not my choice if it's not a covered service. For making that admission, I hope I don't have walk the plank off the CT colonography ship into the merciless tentacles of a vengeful radiology sea monster! So here's hoping that the USPSTF recommendations change before the CTC ship that's taking on water because of holes in our coverage arguments sinks. Discussions about sensitivity, specificity, and invasiveness don't fill those gaps, in my opinion. Equalizing access to screening regardless of geographic location by means of CTC is a moral and socioeconomic imperative I can support. Fighting to overcome barriers to access is a battle I can join. Hand me a bucket and I'll help bail. Let's work to make access to colorectal cancer screening smooth sailing in the future.
For colorectal and other cancer risk assessment tools for use for health care providers and their patients, check out the resources from the NIH National Cancer Institute: