Purpose: The presence of comorbidity in breast cancer patients impacts on treatment choice, toxicity and patients’ outcomes. Whilst comorbidity measurement tools are frequently used by researchers, little is known about their use in clinical practice. The aim of this review was to identify comorbidity measurement tools used in clinical practice, and to examine evidence supporting their role in treatment decision‐making in breast cancer.

Methods: Six electronic databases were searched from inception to 21 March 2019. Quantitative or mixed methods studies that addressed primary treatment of breast cancer and identified a comorbidity measurement tool used in clinical practice at the time of treatment decision making were included. Data was extracted on type of tool utilised, impact of application of tool on patient treatment decisions or outcomes, pattern of use, and psychometric properties.

Results: A systematic search of literature was conducted yielding 752 non‐duplicate studies, and a total of four studies met inclusion criteria. In four studies, comprehensive geriatric assessment was the tool utilised by multidisciplinary teams; one study also calculated pharmacological risk. No studies found direct comorbidity measurement tools utilised independently of geriatric assessment. Geriatric assessment was only utilised in a subset of patients, and the assessment results had a variable impact on treatment modality decisions. The impact of the use of tools on patient mortality and treatment toxicity, the cost effectiveness and psychometric characteristics of the tools were not identified.

Conclusions: There is little evidence on the use of comorbidity tools in clinical decision making in breast cancer. The only tools are indirect and apply to geriatric patients only. Where tools are used, the result does not necessarily change treatment or patient outcome. Further research is needed to identify barriers to comorbidity assessment in clinical practice and to identify comorbidity tools that have the potential to improve patient outcomes.