Fecal immunochemical test less sensitive for detecting proximal lesions

Last Updated: 2018-10-01

By Will Boggs MD

NEW YORK (Reuters Health) - Fecal immunochemical testing (FIT) is less sensitive for detecting proximal than distal advanced neoplasia over multiple rounds of colorectal cancer (CRC) screening, researchers from Italy report.

"At first glance, the most striking result could be the suboptimal results observed in the proximal colon," Dr. Manuel Zorzi from Veneto Tumor Registry and University of Padova, Italy told Reuters Health by email. "However, readers should be also delighted by the impressive performance of repeated FITs in the distal colon and rectum (where 70% of all colorectal cancers are located)."

Previous studies have shown that FIT-based programs are less sensitive in detecting proximal than distal CRC, but these studies considered only a single FIT round.

Dr. Zorzi's team analyzed the long-term detection rates for proximal and distal advanced adenoma and invasive CRC, along with the proportional interval cancer rate (PICR: observed/expected number of incident cases), in their retrospective study of 123,347 participants who had up to six rounds of biennial FIT.

Across all rounds of FIT, the CRC detection rate (per 1000 screened) was significantly higher in the distal colon (0.73) than in the proximal colon (0.45) or rectum (0.47), the authors reported online October 1 in Annals of Internal Medicine.

Detection rates per 1000 screened for both advanced and non-advanced adenoma were also higher in the distal colon (8.38 and 7.01, respectively) than in the proximal colon (3.86 and 6.68) or rectum (2.76 and 1.97).

Detection rates for CRC and adenomas decreased across subsequent rounds, but the reductions were less marked for proximal than for distal and rectal locations.

CRC and advanced adenoma detection rates were higher in men than in women in all locations studied.

Detection rates for CRC and advanced adenoma increased with age, with greater increases for proximal lesions than for rectal or distal lesions.

Overall, 150 colorectal cancers were diagnosed between FIT screenings, with a higher PICR in the proximal colon (25.2%) than in the distal colon (6.0%) or rectum (9.9%).

"Overall," the researchers conclude, "our results indicate that the association between sequential FIT rounds and the natural history of CRC differed according to site, which may be explained by two factors: the site-specific FIT accuracy and age-related right-side shifting."

"Further studies are necessary to identify the best strategy to cope with the specific area of frailty identified by our study," Dr. Zorzi said.

Dr. Chyke A. Doubeni from the University of Pennsylvania in Philadelphia, who co-authored an editorial related to this report, told Reuters Health by email, "Clinicians should know that FIT is an effective screening and is very useful in increasing the uptake of screening and increasing the early detection of colon cancers, but its limitations in detecting right colon cancer should be part of the discussion with patients in choosing among available screening options."

"The FIT is one of the options recommended by the US Preventive Services Task Force to screen for colorectal cancer," he said. "Therefore, clinicians in the U.S. and around the world should remain confident in using the FIT as an important part of the many tools and strategies available to them for averting preventable death from colorectal cancer but recognize its limitations as is the case with all interventions we use in public health and medicine."

Dr. Doubeni added, "Clinicians should remember that patients who have a positive FIT result must undergo colonoscopy (unless there is a clinical reason not to) to realize its benefits. Compared with people receiving timely diagnostic colonoscopy after a positive FIT results, those who do not receive timely follow-up are at much higher risk of dying from colorectal cancer, a potentially avoidable outcome."

Dr. Carlo Senore from SC Epidemiologia, screening, registro tumori - CPO, Turin, Italy recently reviewed the implications for screening of the distribution of colorectal polyps. He told Reuters Health by email, "These results provide additional insight in the natural history of the disease, as they are consistent with previous reports suggesting an age-related right-sided shift of CRCs as well as of adenomas."

"The divergent trend over the six screening rounds of the positive predictive value of FIT for advanced neoplasia, showing a reduction in the distal colon and rectum, while remaining stable in the proximal colon, would also suggest that the prevalence of advanced neoplasia is decreasing with age in the distal segments but not in the proximal colon," he said.

Dr. Senore added, "Considering that several studies already showed that less than 50% of those who attend the initial screening invitation will undergo all the subsequent FIT examination over the following 4-5 rounds, efforts aimed to favor and to promote regular attendance to screening invitations represent a priority, in order to enhance the health impact of screening, which can be substantial, also for proximal colon, as shown by these findings."

SOURCE: http://bit.ly/2NiboUN

Ann Intern Med 2018.