Association Between Time to Colonoscopy After a Positive Fecal Test Result and Risk of Colorectal Cancer and Cancer Stage at Diagnosis

Abstract

Importance: The fecal immunochemical test (FIT) is commonly used for colorectal cancer screening and positive test results require follow-up colonoscopy. However, follow-up intervals vary, which may result in neoplastic progression.

Objective: To evaluate time to colonoscopy after a positive FIT result and its association with risk of colorectal cancer and advanced-stage disease at diagnosis.

Design, setting, and participants: Retrospective cohort study (January 1, 2010-December 31, 2014) within Kaiser Permanente Northern and Southern California. Participants were 70 124 patients aged 50 through 70 years eligible for colorectal cancer screening with a positive FIT result who had a follow-up colonoscopy.

Exposures: Time (days) to colonoscopy after a positive FIT result.

Main outcomes and measures: Risk of any colorectal cancer and advanced-stage disease (defined as stage III and IV cancer). Odds ratios (ORs) and 95% CIs were adjusted for patient demographics and baseline risk factors.

Results: Of the 70 124 patients with positive FIT results (median age, 61 years [IQR, 55-67 years]; men, 52.7%), there were 2191 cases of any colorectal cancer and 601 cases of advanced-stage disease diagnosed. Compared with colonoscopy follow-up within 8 to 30 days (n = 27 176), there were no significant differences between follow-up at 2 months (n = 24 644), 3 months (n = 8666), 4 to 6 months (n = 5251), or 7 to 9 months (n = 1335) for risk of any colorectal cancer (cases per 1000 patients: 8-30 days, 30; 2 months, 28; 3 months, 31; 4-6 months, 31; and 7-9 months, 43) or advanced-stage disease (cases per 1000 patients: 8-30 days, 8; 2 months, 7; 3 months, 7; 4-6 months, 9; and 7-9 months, 13). Risks were significantly higher for examinations at 10 to 12 months (n = 748) for any colorectal cancer (OR, 1.48 [95% CI, 1.05-2.08]; 49 cases per 1000 patients) and advanced-stage disease (OR, 1.97 [95% CI, 1.14-3.42]; 19 cases per 1000 patients) and more than 12 months (n = 747) for any colorectal cancer (OR, 2.25 [95% CI, 1.89-2.68]; 76 cases per 1000 patients) and advanced-stage disease (OR, 3.22 [95% CI, 2.44-4.25]; 31 cases per 1000 patients).

Conclusions and relevance: Among patients with a positive fecal immunochemical test result, compared with follow-up colonoscopy at 8 to 30 days, follow-up after 10 months was associated with a higher risk of colorectal cancer and more advanced-stage disease at the time of diagnosis. Further research is needed to assess whether this relationship is causal.

Figure 1.. Patient flow diagram.

Abbreviations: CRC, colorectal cancer; dx, diagnosis; FIT, fecal immunochemical test; KPNC, Kaiser Permanente Northern California; KPSC, Kaiser Permanente Southern California; n, number.

Figure 2.. Time to colonoscopy after a positive FIT and adjusted risk^a of CRC outcomes (panel A and B).

Abbreviations: Adv-stage, advanced-stage; CI, confidence interval; CRC, colorectal cancer; FIT, fecal immunochemical test. ^aAdjusted for sex; age; race/ethnicity; body mass index; region; FIT screening year; completion of previous FIT screening (ever and in the prior year); and in the year prior to FIT screening, receipt of the flu or pneumonia vaccine, presence of gastrointestinal symptoms (bleeding or blood in stool, unexplained weight loss, abdominal pain, diarrhea, diverticulitis, inflammatory bowel disease, or Lynch syndrome), diagnosis of iron-deficiency anemia or diabetes, current smoker, number of primary care visits, and number of days hospitalized. Models for any CRC include the entire population. Models for advanced adenoma exclude 2,191 patients diagnosed with CRC. Models for advanced-stage CRC exclude 14 patients with CRC of unknown stage. Models for stage-specific CRC exclude patients with CRC of any stage other than the specified stage. The adjusted advanced-stage CRC model dropped 244 patients with unknown BMI because no patient with unknown BMI had this outcome. The adjusted models for CRC stages 0, III, and IV dropped 242 patients with unknown BMI because no patient with unknown BMI had these outcomes. The adjusted CRC stage IV model dropped 2435 patients with unknown race/ethnicity because no patient with unknown race/ethnicity had this outcome.

Figure 3.. Time to colonoscopy after a positive FIT and crude CRC rates (panel A and B).

Abbreviations: Adv-stage, advanced-stage; CI, confidence interval; CRC, colorectal cancer; FIT, fecal immunochemical test.