Impact of COVID-19 pandemic waves on colorectal cancer stage migration and diagnostic delays.

Introduction: The COVID-19 pandemic was associated with substantial changes in cancer diagnosis and treatment. This study aimed to assess changes in colorectal cancer diagnostics during the COVID-19 pandemic by analyzing changes in tumor stage and the number of newly diagnosed cases across different pandemic waves and the post-COVID period using MRI-based data. Methods: The study included 198 patients with colorectal cancer, 43 with a new diagnosis. The study period was divided into five COVID-19-related intervals. The number of newly diagnosed cases across COVID-19 waves was compared using one-way ANOVA. Stage distribution differences were assessed using Fisher's exact test. In follow-up patients, changes were analyzed using the Wilcoxon signed-rank test. Secondary outcomes included tumor changes, number of missed treatments, and the presence of metastases. Results: Monthly averages of newly diagnosed colorectal cancer cases were lower during the COVID-19 waves than in the post-COVID period (p < 0.001). Although overall tumor stage did not differ between waves, larger tumors were more frequent during the COVID-19 waves, whereas early-stage (T1) tumors were more common in the late/post-COVID period (p < 0.001). Tumor stage distribution also differed between the COVID and post-COVID periods, with a shift toward earlier-stage disease after the pandemic (p = 0.002). No differences were observed in missed treatments across COVID-19 periods (p-value > 0.05). Discussion: The COVID-19 pandemic was associated with a lower number of newly diagnosed colorectal cancer cases during the pandemic and a higher proportion of patients presenting with more advanced disease stages. These findings suggest an association with pandemic-related healthcare disruption; however, causality cannot be established. Trial registration: https://clinicaltrials.gov/, identifier NCT07328399.