A fecal immunochemical test (FIT)-based program involving six rounds of screening yielded a negligible reduction in detection rates for neoplastic lesions in the proximal versus the distal colon after the first round, a study found.
To assess the long-term detection rates with FIT for advanced adenoma and colorectal cancer by anatomical location, researchers conducted a population-based, organized screening program in Italy among patients ages 50 to 69 years who completed six rounds of FIT screening. At each screening round, the detection rates for advanced adenoma and cancer, as well as the proportional interval cancer rate, were calculated by location in the proximal colon, distal colon, or rectum. The results of the study were published by Annals of Internal Medicine on Oct. 2.
Between 2002 and 2014, 123,347 participants underwent 441,647 FITs. The numbers of advanced adenomas and cancer cases detected were 1,704 and 200 in the proximal colon, 3,703 and 324 in the distal colon, and 1,220 and 209 in the rectum, respectively. The detection rate for proximal colon cancer declined only from the first to the second screening round (0.63 to 0.36 per 1,000 persons screened), while the rate for both distal colon and rectal cancer steadily decreased across six rounds (1.65 per 1,000 persons screened in the first round to 0.17 per 1,000 persons screened in the sixth round for the distal colon and 0.82 per 1,000 persons screened in the first round to 0.17 per 1,000 persons screened in the sixth round for the rectum).
Similar trends were seen for advanced adenoma (5.32 per 1,000 persons screened in the first round to 4.22 per 1,000 persons screened in the sixth round for the proximal colon and 15.2 per 1,000 persons screened in the first round to 5.02 per 1,000 persons screened in the sixth round for the distal colon). Overall, 150 cases of interval cancer were diagnosed. The proportional interval cancer rate was higher in the proximal colon (25.2%; 95% CI, 19.9% to 31.5%) than in the distal colon (6.0%; 95% CI, 3.9% to 8.9%) or rectum (9.9%; 95% CI, 6.9% to 13.7%).
“Despite our study's evidence of a much greater long-term FIT-related benefit for distal [colorectal cancer] prevention, FIT is not completely ineffective in the proximal colon,” the authors wrote. “In fact, a relevant reduction in detection rate for invasive [colorectal cancer] and advanced adenoma also was observed in the proximal colon, but most of the decrease occurred between the first and second screening rounds.”
An editorial noted that FIT may be less effective in the right colon because of lesions that grow more rapidly and that bleed less, or because a longer transit time may degrade hemoglobin, making occult bleeding undetectable.
“However, lower sensitivity in detecting right colon lesions is a shared limitation across all current [colorectal cancer] screening strategies,” the editorial stated. “Most interval cancer cases occur in the right colon, regardless of testing strategy, although colonoscopy has become better at detection through quality and technologic improvements.”