After the first round of a fecal immunochemical test (FIT)-based, multiple-round, long-term screening program, there is a negligible reduction in detection rates for neoplastic lesions in the proximal versus the distal colon, according to a study published online Oct. 2 in the Annals of Internal Medicine.

In Europe, several colorectal cancer (CRC) screening programs are based on the fecal immunochemical test (FIT). This strategy has consistently demonstrated both high sensitivity for detecting advanced adenoma and invasive CRC and good adherence by the target population.

Despite a lack of randomized trials, the available evidence suggests that FIT-based CRC screening may reduce cancer mortality through both diagnostic anticipation and the detection and removal of advanced adenomas during post-FIT colonoscopy.

FIT-based screening program

When considering biennial FIT screening, long-term efficacy may be assessed by calculating the cumulative detection of both advanced adenoma and CRC. The results of a long-term, FIT-based screening program in Italy showed a statistically significant reduction in CRC detection across 6 screening rounds, with the decrease in the advanced adenoma detection rate being much less pronounced and restricted only to the second round

Manuel Zorzi, M.D., from the Veneto Tumour Registry in Padova, Italy, and colleagues conducted a retrospective study involving persons aged 50 to 69 years who completed six rounds of FIT screening and assessed long-term detection rates for advanced adenoma and colorectal cancer.

The researchers found that a total of 123,347 participants had 441,647 FITs between 2002 and 2014. From the first to the second screening round, the detection rate for proximal colon cancer declined (0.63 to 0.36 per 1,000 screenees); across six rounds, there was a steady decrease in distal colon and rectal cancer (distal colon: 1.65 in the first round to 0.17 in the sixth round; rectum, 0.82 in the first round to 0.17 in the sixth round).

For advanced adenoma, similar trends were found. One hundred fifty cases of interval cancer were diagnosed. The proportional interval cancer rate was higher in the proximal colon than the distal colon or rectum (25.2 versus 6.0 or 9.9%, respectively).

"This FIT-based, multiple-round, long-term screening program had a negligible reduction in detection rates for neoplastic lesions in the proximal versus the distal colon after the first round," the authors write.

Several authors disclosed ties to the pharmaceutical and imaging industries. In the present FIT-based CRC screening program, the significant long-term reduction in detection rate for advanced distal neoplasia paralleled a much smaller reduction in the detection of advanced proximal neoplasia. At the same time, a higher PICR was observed for proximal versus distal cancer.

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

The modest reduction in long-term detection rates for proximal advanced neoplasia, particularly invasive CRC, with the repeated FIT and the higher PICR in the proximal colon indicate that FIT-based programs have suboptimal efficacy in preventing the age-related rightward shift of CRC.