Background The COVID-19 pandemic impacted Dutch society and the healthcare system. Focus switched to care for COVID-19 patients, thereby altering care for non-COVID patients. Non-urgent medical visits were cancelled or postponed and patients were reluctant to visit healthcare services.Objectives This study aimed to investigate the impact of the COVID-19 pandemic on trends in diagnoses of keratinocyte carcinoma (cutaneous squamous cell carcinoma (cSCC), basal cell carcinoma (BCC)) and to assess the magnitude of diagnostic delays. MethodsThe number of cSCC and BCC diagnoses in each month of 2020 was compared to the expected number of diagnoses for these months, using data from the Netherlands Cancer Registry. Expected diagnoses for 2020 were used as a reference to take the yearly increase in keratinocyte carcinoma incidence into account and were calculated by extrapolating the trends observed in 2017-2019. Comparisons were further stratified by age, sex and region. Estimates of diagnostic delays were calculated and corrected for the influence of excess mortality due to the pandemic on keratinocyte carcinoma incidence. ResultsThe number of cSCC and BCC diagnoses substantially decreased when compared to the number of diagnoses expected from March to May 2020 (cSCC À29%, BCC À50%). These decreases were observed across all age groups, both sexes, and all regions. From June to September the number of cSCC and BCC diagnoses was higher than expected, after which it slightly dropped below expected in October to December. In total, 2020 keratinocyte carcinoma diagnoses continued to trail those expected, with a backlog of around 1150 cSCCs and 11 767 BCCs remaining at the end of the year. ConclusionDiagnosis of keratinocyte carcinoma was suboptimal during the COVID-19 pandemic, due to diagnostic delays likely resulting from both patient and health system-related delay. Further studies will need to determine the effects of these diagnostic delays on outcomes.

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