Evaluation of breast cancer screening programmes present results in terms of cost per QALY but fail to include any disutility for patients who may have been overdiagnosed and receive unnecessary treatment. Ductal carcinoma in situ (DCIS) is a heterogeneous disease likely to account for a large proportion of overdiagnosis. This thesis presents an overview of the challenges associated with valuing breast cancer states, using quantitative and qualitative evidence to demonstrate that the inclusion of the harm from overdiagnosis is important in the economic evaluation of breast cancer interventions.

A systematic review found the utilities informing breast screening policy were unlikely to fully capture all benefits and risks. An empirical study deriving utilities from 172 women for health states explicitly describing DCIS treatment were lower than those from the literature, where it is unlikely that individuals were informed treatment may be unnecessary. The utilities were applied in an illustrative model and suggested this disutility had the potential to change the cost-effectiveness of treating low-risk, screen detected disease. Qualitative interviews of 26 patients validated overdiagnosis was important in treatment decisions. This thesis contributes important methodological considerations for modelling breast cancer interventions and suggests future research to validate this harm in economic evaluations.