Background: COVID-19 has significantly disrupted cancer care delivery, with potential implications on patient outcomes and disease management. While prior studies have observed declines in cancer screenings and cancer-related encounters following COVID-19, less is known about broader treatment outcomes for patients with cancer. Moreover, examining nationwide trends in care delivery allows health systems and providers to identify barriers to high-value care and improve existing practices. Consequently, we use nationally representative data to assess the impact of COVID-19 on the timeliness of care for breast, lung, and colorectal cancer – three leading causes of cancer death in the United States. Methods: We performed a retrospective analysis of adults in the National Cancer Database who were diagnosed with primary breast, lung, and colorectal cancer between January 1, 2017, and December 31, 2021. The primary goal was to determine differences in time to treatment initiation (TTI), defined as the number of days between initial diagnosis and the date of first surgery, radiation, or systemic treatment. Patients who did not yet receive treatment or died during the analytic period were censored. Cox proportional hazards regression models, adjusting for sociodemographic and clinical variables, generated hazard ratios (HRs) with 95% CIs to assess the impact of a pre-COVID (2017-2019) or COVID (2020-2021) cancer diagnosis on TTI. Results: Of 1,635,644 patients with cancer that met inclusion criteria, 999,498 (61.1%) were diagnosed in the pre-COVID period and 636,084 (38.9%) were diagnosed in the COVID period. There was a decrease of 38,380 new cancer cases between 2019 and 2020. The median TTI for the pre-COVID cohort was 35 (IQR: 22-52) days while the median TTI for the COVID cohort was 36 (IQR: 24-55) days. Upon adjusting for covariates, however, TTI for the COVID cohort was shorter than that of the pre-COVID cohort (HR: 1.01, 95% CI [1.01-1.02], p < 0.001). Subgroup analyses by cancer type showed similar, shorter TTI for patients with breast cancer (HR: 1.02, 95% CI [1.01-1.02], p < 0.001). Based on significant interaction terms, we found shorter TTI during COVID for patients of Black (HR: 1.02, 95% CI [1.01-1.03], p < 0.01) and Asian (HR: 1.06, 95% CI [1.03-1.09], p < 0.001) race, as well as Hispanic ethnicity (HR: 1.03, 95% CI [1.01-1.05], p < 0.001). White patients did not have significant changes in TTI during COVID (HR: 1.00, 95% CI [0.99-1.01], p > 0.05).These results persisted in sensitivity analyses by treatment type. Conclusions: There was a decrease in the number of new diagnoses of breast, lung, and colorectal cancer during COVID compared to pre-COVID. Among those with new diagnoses, the COVID-19 pandemic was not associated with delays to necessary care or stark disparities among patients diagnosed with three common cancers, showcasing the resilience of oncology care during the public health emergency.