Background
Control measures implemented during the COVID-19 pandemic, such as service re-organisation, staff redeployment, increases in remote consultations in primary care, and pauses in national screening programmes may have disrupted diagnostic pathways. The number of primary care consultations also declined in the early months of the pandemic due to concerns about contracting COVID-19 combined with a reluctance to burden healthcare professionals. There has been some concern that these changes would result in an increase in those presenting with later stage disease.   
Objectives
To compare the stage at diagnosis of the five most common cancers (prostate, female breast, lung, colorectal and melanoma) during the pandemic period (2020 and 2021) to cases diagnosed pre-pandemic (2018-2019).
Methods
Data on cancers diagnosed 2018-2021 were extracted from the National Cancer Registry Ireland (NCRI). Stage at diagnosis was recorded using TNM7th edition. For each individual cancer type and stage I-IV, incidence rate ratios (IRRs) were estimated using negative binomial regression. Models included case count as the outcome, total population as an offset, and the following covariates: age group (<50, 50–69, 70+ years), sex, and diagnosis period (baseline: average 2018–2019; and years 2020 and 2021).  Cases with unknown stage were excluded from the analyses and the underlying population offset was adjusted accordingly. Model fit was assessed using Akaike’s Information Criterion (AIC) and plots of standardised residuals versus predicted case count.
Percentage change (PC) in IRRs was calculated using the following formula: PC=[IRR-1]*100 and the 95%CIs were converted in a similar manner.
Results
Prostate cancer incidence rates decreased significantly from the baseline rate (2018-2019) across all stages (stage I -10%, stage II -9%, stage III -19% and stage IV -13%) in 2020. Rates of stage I (-9%) and stage II (-16%) prostate cancer continued to be significantly lower in 2021 compared to the baseline rate.
For female breast cancer the stage specific incidence rates decreased significantly for stage I (-2%), II (-12%) and III (-13%) in 2020. Stage specific rates in 2021 did not differ significantly from the baseline rates.
Lung cancer incidence showed significant reductions in stage II (-27%) and stage III (-17%) in 2020, with the incidence of stage III lung cancer remaining below pre-pandemic levels (by -19%) in 2021. 
For colorectal cancer the stage specific incidence rates decreased significantly across stage I (-25%), II (-28%) and III (-17%). No significant changes were observed in stage-specific rates in 2021.
There were no significant changes in stage specific incidence rates of melanoma in 2020 or 2021.
Conclusions/implications
Decreases in stage-specific incidence rates were observed for early stage cancer (stage I and/or stage II) in four of the five cancers examined in 2020. No evidence of any increases in later stage cancers (stage III or IV) was observed in either 2020 or 2021.The changes in stage-specific incidence rates reflect diagnostic interruptions (e.g. screening and opportunistic testing) in prostate, breast, colorectal and lung cancer. Nevertheless, for most part, this impact was immediate and not prolonged, suggesting that the cancer care system remained resilient through the pandemic.