CT Colonoscopy Image Source: TeraRecon

CT colonography (CTC) is an alternative to colonoscopy that is less invasive, better tolerated and provides good diagnostic accuracy for patients who have an increased risk or familial history of colorectal cancer, according to a study in the June 17 issue of the Journal of the American Medical Association.

Emily Finlayson, MD, from the University of Michigan in Ann Arbor, who commented on the study's findings in an accompanying editorial, told Health Imaging News that the main differentiator in this trial is that the researchers examined screening higher risk patients, whereas previous trials have studied screening average risk patients.

"This is really the first study to assess the effectiveness of CTC in higher risk patients," she said. "The researchers also stratified study participants by their diagnosis--whether they have a blood test or a history of a polyp--which took it a step beyond for CTC indications for use."

Individuals at increased risk of colorectal cancer (CRC) include those with a first-degree family history of advanced colorectal neoplasia and those with positive results from fecal occult blood tests (FOBT).

"However, adherence to follow-up colonoscopy in these individuals is suboptimal," the study authors wrote. "Being less invasive and thus more tolerable, CTC may increase acceptability and adherence to screening, but little information is available on its performance."

Daniele Regge, MD, of the Institute for Cancer Research and Treatment, Candiolo in Turin, Italy, and colleagues assessed the accuracy of CTC in detecting advanced colorectal neoplasia in asymptomatic individuals at increased risk of CRC using colonoscopy as the reference standard.

The multicenter study included individuals at increased risk of CRC due to either family history of advanced neoplasia in first-degree relatives, personal history of colorectal adenomas or positive results from FOBTs. Each participant underwent CTC followed by colonoscopy on the same day.

Of 1,103 participants, 937 were included in the final analysis: 373 cases in the family-history group, 343 in the group with personal history of adenomas and 221 in the FOBT-positive group. The prevalence of advanced neoplasia was 7.5 percent in the family-history group; 11.1 percent in the post-polypectomy group; and 50.2 percent in the FOBT-positive group.

Overall, CTC identified 151 of 177 participants with advanced neoplasia 6 mm or larger (sensitivity, 85.3 percent) and correctly classified results as negative for 667 of 760 participants without such lesions (specificity, 87.8 percent), according to the authors.

The positive and negative predictive values were 61.9 percent and 96.3, respectively. The negative predictive value ranged between 84.9 percent in the FOBT-positive group and 98.5 percent in the family-history group.

Finlayson noted that the centers that participated in the trial had "state of the art equipment, along with radiologists with substantial experience interpreting these images, so it's unclear whether these results can be replicated across all centers."

Based on their findings, the study authors concluded that these results indicate a "potentially effective use of CTC as an alternative to colonoscopy for screening individuals with family history of advanced colorectal neoplasia. CTC has been shown to be better accepted than colonoscopy and has a negligible risk of serious adverse events; thus, it may help increase the low adherence reported for individuals who are candidates for screening, which is the main negative factor affecting its efficacy in reducing mortality from CRC."

Finlayson said that this study should be the first of other studies to evaluate CTC as a screening tool in this higher risk population.

"It's a bit hasty to make a policy or guideline decision based on the findings of one study," she noted. "However, this study could serve as a basis to evaluate CTC for this indication."

In the accompanying editorial, Finlayson wrote that while the use of CTC as "a screening and surveillance modality is still a matter of debate, the study by Regge et al suggests that CTC may be an acceptable alternative to colonoscopy in patients with a history of adenoma and those with a family history of colorectal neoplasm.

"The question remains whether clinicians are willing to accept a study with decreased sensitivity for the potential of increased adherence with recommended screening and surveillance guidelines. With the majority of individuals in the United States who meet criteria for colorectal cancer screening and surveillance not undergoing recommended procedures, an imperfect test that has a lower risk profile and greater acceptance among patients seems to be an appealing solution."

Despite the recent CMS decision to decline reimbursements for CTC as a screening modality across all patient populations, Finlayson said that the "totality of the evidence is pointing to using CTC as a reasonable alternative to colonoscopy. Also, we don't currently have people to perform colonoscopies or enough centers to provide that service for those people, 50 years or older, that would be eligible for a screening."

She also observed that there are a number of eligible patients who refuse colonoscopies due to its invasive nature.

"Considering the other medical tests that the U.S. reimburses for, which have far less evidence, CMS may want to reconsider its decision," she noted.

Based on the findings of this and previous trials, Finlayson said that "CTC, which is slightly less accurate, is the best second choice for colorectal cancer screening."