A Comparison of the Renal Cell Carcinoma-Symptom Index (RCC-SI) and the Functional Assessment of Cancer Therapy-Kidney Symptom Index (FKSI)

The development and validation of measures that provide disease-specific, patient-reported outcomes have become increasingly relevant in the care of cancer patients, especially for assessing symptoms from the patient's perspective. Recently, two patient symptom questionnaires were developed for kidney cancer patients, the Renal Cell Carcinoma-Symptom Index (RCC-SI) and the Functional Assessment of Cancer Therapy-Kidney Symptom Index (FKSI). This article describes the development of the revised FKSI scale (FKSI-19) and reconciles its use with the RCC-SI. Fifty participants with advanced kidney cancer commented on their symptoms and concerns about kidney cancer and this input was used to revise FKSI items. These patients also completed the RCC-SI, the Functional Assessment of Cancer Therapy-General (FACT-G), and an older version of the FKSI scale. We qualitatively reviewed item wording and content coverage across the two instruments, examined correlations between the scales, and calculated basic psychometrics on each scale. We found that the FKSI-19 and the RCC-SI addressed similar symptoms. Qualitative and descriptive statistical analyses demonstrated considerable overlap between the two instruments (rho=0.88, P<0.001). Cronbach's alpha for the FKSI-19 and RCC-SI were both good, at 0.86 and 0.92, respectively. The FKSI-19 has some advantages over the RCC-SI. The FKSI-19 has more clarity in item phrasing, is shorter in length, and covers a similar breadth of disease-based symptoms when compared to the RCC-SI.