Purpose: To investigate whether the COVID-19 pandemic and national lockdown had an impact on the extent of cancer disease at staging using FDG PET/CT as surrogate marker.Methods: Retrospective observational study including cancer patients submitted to FDG PET/CT for staging purposes from June 1 to October 31, 2020, and June 1 to October 31, 2021, respectively. Data regarding primary tumour, nodal (N) status and number of involved nodal stations, presence and number of distant metastases (M) were collected. Each scan was classified in limited vs advanced status. Data were aggregated across the study population and tumour type. Bi-weekly frequencies of the observed events were analysed. Results: 611 patients were included in the study (240 in 2019 vs. 371 in 2020, respectively). A significant increase in the rate of advanced disease patients in 2020 compared to 2019 was found (rate 1.56, p<0.001) as well as in the rate of N+ or M+ patients (rate 1.84 and 2.09 respectively, p<0.001) and in the rate of patients with a greater number of involved N stations or M (rate 2.01 and 2.06 respectively, p<0.001). Analysis by tumour type showed a significant increase of advanced disease, N+ or M+ status and number of involved N stations or M in lung cancer and lymphoma in 2020 compared with 2019 (p<0.003). Advanced disease rate resulted also significantly increased in gynaecologic cancer and N rate was significantly increased in gastro-intestinal cancer (p<0.05). Conclusion: The rate of cancer patients with advanced disease at staging FDG PET/CT increased by 1.5-fold in 2020, following the national lockdown due to the COVID-19 pandemic, compared to 2019 with a significant increase of patients with N involvement or M. Targeted health interventions are needed to mitigate the effects of the pandemic on patient outcome.