Background: The COVID-19 pandemic led to a significant reduction in the provision of screening, case identification and hospital referrals to cancer patients. To our knowledge, no study has yet correlated quantitatively the consequences of these limitations for cancer patient management. This study evaluates the implications of such reductions for patients newly diagnosed with metastatic colorectal cancer (mCRC) in both the pre- and post-lockdown periods. Methods: We examined 80 newly identified mCRC patients from 18 different clinical centers. These cases come from the screening procedure of a clinical trial which is using circulating DNA (cirDNA) analysis to determine their RAS and BRAF status. Results: The tumor burden as evaluated by the median total plasma cirDNA concentration showed a statistically higher level in patients diagnosed post-lockdown compared to those diagnosed pre-lockdown (119.2 versus 17.3 ng/mL; p<0.0001). In order to link tumor burden to survival, we compared the survival of these mCRC patients with previous studies in which cirDNA was examined in the same way (median survival, 16.2 months; median follow up, 48.7 months, N=135). Given the poor survival rate of mCRC patients with high cirDNA levels (14.7 vs 20.0 and 8.8 vs 19.3 months median survival when dichotomizing the cohort by the median cirDNA concentration 24.4 and 100 ng/mL, respectively), our study points to the potential deleterious consequences of the COVID-19 pandemic. Conclusions: Recognizing that our exploratory study offers a snapshot of an evolving situation, our observations nonetheless clearly highlight the need to determine actions which would minimize delays in diagnosis during the ongoing and future waves of COVID-19.