Challenging the current norm: Does health related quality of life data from reference populations accurately reflect baseline values in breast cancer patients? An observational cohort study comparing EORTC QLQ-C30 scores between the general Swedish population and baseline scores in breast cancer patients

Background: Increased overall survival in breast cancer patients has led to a growing recognition of long-term effects of cancer treatment of patients' quality of life. Health related quality of life (HRQoL) data, as measured by patient reported outcome measures (PROMs), is increasingly incorporated into clinical practice and research. A commonly used method current available to interpret HRQoL PROMs data is by comparison to reference values, often obtained from sampling of the general population. The aim of this study was to assess whether HRQoL reference values derived from the general population are an accurate representation of the baseline values of an outpatient breast clinic population.

Methods: A prospective observational cohort study was conducted by obtaining EORTC QLQ-C30 values for all patients offered an appointment in the outpatient breast clinic. These results were then compared to published baseline values in the general Swedish population, matched by gender and age.

Results: 568 questionnaires were returned with a response rate of 81,1 %. The outpatient breast clinic cohort reported a higher grade of symptoms, lower function and lower quality of life compared to the equivalent reference population.

Conclusion: This study challenges the assumption that the reference values accurately reflect those of the study population which clinicians and researchers need to account for in study design and clinical practice.