Development and validation of a scale to measure disease-related symptoms of kidney cancer

Objectives: Using patient and expert provider input, we previously developed a 15-item index of the most important symptoms and concerns of people being treated for advanced kidney cancer, the Functional Assessment of Cancer Therapy - Kidney Symptom Index (FKSI). These 15 concerns are a mixture of disease-related symptoms and treatment-related side effects. As a result, it may be difficult to assign an informative label to the score defined as the summation of these 15 most important concerns. Because one of the primary goals of treating advanced kidney cancer is the relief of disease-related symptoms, we set out to differentiate from the list of 15 symptoms those that are predominantly attributable to kidney cancer itself rather than its treatment, and to evaluate this abbreviated FKSI - Disease-Related Symptoms (FKSI-DRS). Methods: Survey results from 18 experienced clinical experts were summarized to separate DRS from other concerns more arguably attributable to treatment side effects. This nine-item FKSI-DRS was then validated on a sample of 141 people with kidney cancer. Results: The FKSI-DRS is reliable (internal consistency range = 0.75-0.78; test-retest reliability intraclass correlation = 0.85), and valid, separating groups by performance status and the patient's own global rating of change. The likely minimally important difference in the FKSI-DRS is in the range of 2-3 points. Conclusions: The FKSI-DRS is a reliable, valid, and responsive brief index of the most important symptoms associated with advanced kidney cancer.