Shim, S., Kang, D., Kim, N., Han, G., Lim, J., Kim, H., Park, J., Lee, M., Lee, J. E., Kim, S. W., Yu, J., Chae, B. J., Ryu, J. M., Nam, S. J., Lee, S. K., Cho, J.
PURPOSE: Little is known about the impact of financial toxicity in disease-free breast cancer survivors. We aim to validate the COST in Korean (COST-K) and evaluate financial toxicity among disease-free breast cancer survivors. MATERIALS AND METHODS: We conducted linguistic validation following a standardized methodology recommended by FACITtrans. For psychometric validation, we conducted a cross-sectional survey with 4,297 disease-free breast cancer survivors at a tertiary hospital in Seoul, Korea between November 2018 and April 2019. Survivors were asked to complete the COST-K and EORTC QLQ-C30 questionnaires. The test-retest reliability, internal consistency, and validity of the COST-K were assessed using standard scale construction techniques. RESULTS: The COST-K demonstrated good internal consistency, with a Cronbach’s α of 0.81. The test-retest analysis revealed an intraclass correlation coefficient of 0.78. The COST-K had moderate correlation (r = -0.60) with the financial difficulty item of the EORTC QLQ-C30 and week correlation with the items on acute and chronic symptom burdens (nausea/vomiting = -0.18, constipation = -0.14, diarrhea = -0.14), showing good convergent and divergent validity. The median COST-K was 27 (range, 0-44; mean ± SD, 27.1 ± 7.5) and about 30% and 5% of cancer survivors experienced mild and severe financial toxicity, respectively. Younger age, lower education, lower household income was associated with higher financial toxicity. CONCLUSION: The COST-K is a valid and reliable instrument for measuring financial toxicity in disease-free breast cancer survivors. Considering its impact on the HRQOL, more studies need to be conducted to evaluate financial toxicity in cancer survivors and design interventions.