INTRODUCTION: After colorectal cancer (CRC) treatment, patients undergo five-year follow-up involving carcinoembryonic antigen (CEA) tests, imaging, and colonoscopies. This retrospective cohort study explores adherence to the CRC follow-up guideline in the Netherlands until 2021 and its association with treatment of recurrences with curative intent. METHODS: Stage II/III CRC patients with recurrent disease within 3 years after diagnosis were selected from the Netherlands Cancer Registry (n = 430). Adherence to CEA tests, imaging, and colonoscopy was classified as 'according to/more follow-up' or 'less follow-up' than recommended. Logistic regression analyses examined factors associated with receiving less follow-up and the relationship between 'follow-up adherence' and 'treatment with curative intent', potentially mediated by 'mode of detection' (symptomatically vs. routine test). RESULTS: In total, 18.3% patients had fewer CEA tests, 41.4% fewer imaging, and 56.1% fewer colonoscopies than recommended. Factors associated with fewer follow-up moments were tumor localization, age (≥ 75 years), comorbidities, tumor differentiation and adjuvant chemotherapy. Patients receiving fewer CEA tests faced 4.8 times higher odds (95% CI: 2.9-8.1) of symptom-detected recurrence and were less likely to be curatively treated (OR = 0.5
95% CI: 0.3-0.9). Mediation analysis indicated a significant average causal mediation effect (p = 0.003), emphasizing the mediating role of mode of detection. Receiving fewer imaging and colonoscopies showed insignificant total effects on treatment with curative intent. CONCLUSION: Our findings offer insights into follow-up adherence, detection mode, and treatment with curative intent. The discovery that adherence was highest for CEA, along with the correlation between CEA adherence and treatment with curative intent, aligns with the recent adaptation of guidelines emphasizing CEA measurement over imaging.