People diagnosed with cancer during the first two years of the COVID-19 pandemic had worse short-term survival compared to patients diagnosed in 2015-2019. A population-based cohort study found this. The study suggests that disruptions caused by the pandemic worsened cancer survival. Processes were disrupted for early cancer diagnosis. Patients diagnosed in the pandemic were more likely to have an advanced tumor stage than in 2019. In the Czech Republic, the incidence of new cancer cases decreased in 2020, with a recovery lasting until 2022. These changes led to higher mortality from oncological diseases.