Delayed Colonoscopy Following a Positive Fecal Test Result and Cancer Mortality

Abstract

Background: A fecal test followed by diagnostic colonoscopy for a positive result is a widely endorsed screening strategy for colorectal cancer (CRC). However, the relationship between the time delay from the positive test to the follow-up colonoscopy and CRC mortality has not been established.

Methods: From a population-based screening program, we identified CRC patients newly diagnosed from 2005 through 2015 by a positive fecal occult test followed by a colonoscopy. The primary outcome measure was CRC-specific mortality according to four categories for the time elapsed between the positive result and the subsequent colonoscopy.

Results: The 1749 patients underwent colonoscopies within 0-3 months (n = 981, 56.1%), 4-6 months (n = 307, 17.5%), 7-12 months (n = 157, 9.0%), and later than 12 months (n = 304, 17.4%). CRC-specific deaths according to exposure groups were: 13.8% (135 of 981) for 0-3 months, 10.7% (33 of 307) for 4-6 months (crude hazards ratio [HR] = 0.74, 95% confidence interval [CI] = 0.51 to 1.14), 11.5% (18 of 157) for 7-12 months (crude HR = 0.83, 95% CI = 0.51 to 1.42), and 22.7% (69 of 304) for longer than 12 months (crude HR = 1.40, 95% CI = 1.04 to 1.90). The only variable that was associated with mortality risk was the number of positive slides (P = .003). High positivity was twice the value in the 0-3 as the longer-than-12 months group: 51.9% vs 25.0% and similar for the 4-6 and 7-12 months groups (38.1% and 36.5%), respectively. The adjusted HRs for CRC mortality were 0.81 (95% CI = 0.55 to 1.19); 0.83 (95% CI = 0.50 to 1.41), and 1.53 (95% CI = 1.13 to 2.12, P = .006) for the 4-12, 7-12, and longer-than-12-months groups, respectively, compared with the shortest delay group.

Conclusions: Among screen-diagnosed CRC patients, performance of colonoscopy more than 12 months after the initial positive fecal occult blood test was associated with more advanced disease and higher mortality due to CRC.

Figure 1.

Selection of the study population. The source population comprises all 50- to 74-year-old individuals who were screened by fecal occult blood test (FOBT) during the study period. The study population comprises newly diagnosed screen-detected colorectal cancer (CRC) cases without anemia before the screening process. The four exposure groups denote the time delay from the positive FOBT result to diagnostic colonoscopy in months. CHS = Clalit Health Services; IBD = inflammatory bowl disease.

Figure 2.

Percentage of Surveillance, Epidemiology and End Results (SEER) coding of colorectal cancer (CRC) cases in fecal occult blood test (FOBT)-positive patients according to time to diagnostic colonoscopy. Shown are the percentages of individuals diagnosed with each SEER code disease stage for each of the four exposure groups. The four exposure groups denote the time delay in months from the positive FOBT result to diagnostic colonoscopy. The numbers above the columns represent the number of patients in each subgroup. The missing stage data are represented separately. Explanation of SEER coding is included in the footnote.

Figure 3.

Cumulative incidence of colorectal cancer (CRC) mortality in fecal occult blood test (FOBT)-positive patients according to time to diagnostic colonoscopy. Shown are the cumulative incidence CRC mortality rates according to the time to diagnosis for each of the four exposure groups. The four exposure groups denote time delay from the positive FOBT result to diagnostic colonoscopy in months. The table below the survival curves figure shows the numbers at risk for each exposure group according to years of follow-up.