OP173 Cancer stage migration and treatment initiation: a modelling study evaluating the impact of the COVID-19 pandemic on cancer outcomes in Ireland

Background Cancer services in Ireland were significantly disrupted during the COVID-19 pandemic. Using an epidemiological modelling approach, this study aimed to investigate the impact of delays in time to treatment initiation (TTI), due to the pandemic, on stage of disease for breast and lung cancer and associated excess deaths in Ireland. Methods The inverse stage-shift model described by Degeling et al. (2021) was used. Data on estimated distribution of cancer stage at diagnosis, net survival at one to five years post diagnosis for all ages from 2014 to 2018 and projected cancer incidence for 2020, were ascertained for breast and lung cancer from the National Cancer Registry in Ireland. The primary outcome was the probability of an upward stage migration from stage I to stage II and from stage II to III, based on the association between hypothetical delays in TTI of 3 or 6-months. Excess deaths within five years from diagnosis were estimated. Results For breast cancer, the probability of migration from stage I to stage II was 0.13 and 0.25, and the estimated number of excess deaths after five years were 2 and 6 for a 3- and 6-month delay in TTI respectively. The probability of migration from stage II to stage III was 0.09 and 0.17, and the estimated excess deaths were 7 and 27 respectively. For lung cancer, the probability of migration from stage I to stage II was 0.50 and 0.75 and the estimated excess deaths were 15 and 44 for a 3- and 6-month delay in TTI respectively. The probability of stage II to stage III migration was 0.30 and 0.52, and estimated excess deaths were 18 and 56 for a 3- and 6-month delay in TTI respectively. Conclusion These preliminary modelling analyses suggested that delays in TTI of 3 and 6 months would produce an upward stage migration and excess deaths in those with breast and lung cancer in Ireland. The provision of cancer treatment services during the pandemic was interrupted by restrictions and physical distancing policies, which potentially increased the TTI. Prevention of upward stage migration and improving health system resilience are crucial to optimising cancer care. Further validation of the model is required to investigate the long-term impact of the COVID-19 pandemic on cancer outcomes.