This study modeled the impact of different scenarios of COVID-19 lockdown-accumulated backlog in cancer referrals on cancer survival. Results suggest that, for many cancer patients, treatment delays of 2-6 months will lead to a substantial proportion of patients with early-stage tumors progressing from having curable to incurable disease. Results also indicate that even small delays (e.g., 2 months) can lead to substantial survival decrements among younger patients; among adults 70 years of age and older, balancing risk of death between cancer and COVID-19 is important.