Many people delayed care or were unable to get care during the first year of the COVID-19 pandemic. This study estimates the missed diagnoses of screenable cancers from March to December 2020. Diagnoses of included cancers were 6% lower than would be expected, even 10 months after the start of the pandemic. The greatest decrease was seen in prostate cancer, followed by breast and lung cancers, with an overall estimate of more than 134,000 missed cancer diagnoses.