  We propose a methodology to quantify the impact on breast cancer mortality of
diagnostic delays caused by public health measures introduced as a response to
the COVID-19 pandemic. These measures affected cancer pathways by halting
cancer screening, delaying diagnostic tests, and reducing the numbers of
patients starting treatment. We introduce a semi-Markov model, to quantify the
impact of the pandemic based on publicly available population data for women
age 65{89 years in England and relevant medical literature. We quantify
age-specific excess deaths, for a period up to 5 years, along with years of
life expectancy lost and change in cancer mortality by cancer stage. Our
analysis suggests a 3-6% increase in breast cancer deaths, corresponding to
more than 40 extra deaths, per 100,000 women, after age 65 years old over 5
years, and a 4-6% increase in registrations of advanced (Stage 4) breast
cancer. Our modelling approach exhibits consistent results in sensitivity
analyses, providing a model that can account for changes in breast cancer
diagnostic and treatment services.
