OBJECTIVES: The Functional Assessment of Cancer Therapy–Kidney Symptom Index Disease-Related Symptoms (FKSI-DRS) is useful tool to gauge clinical benefit in metastatic renal cell carcinoma (mRCC). This study aimed to estimate important difference (ID) in FKSI DRS scores that is considered to be meaningful when comparing treatment effect between groups, using mRCC trial data.

METHODS: Data were derived from two pivotal phase III mRCC trials comparing sunitinib versus interferon-alfa (N=750) in first-line mRCC, and axitinib versus sorafenib (N=723) in second-line mRCC. The change from baseline in FKSI-DRS score was examined as a function of an adverse event (AE) grade using a longitudinal repeated measures model (RMM); several types of adverse events were analyzed. In sensitivity analyses, using the same methodology, we examined the relationship between change in FKSI-DRS score as an outcome and two additional anchors: the FKSI item “I am bothered by side effects of treatment” score and change from baseline in EuroQoL (EQ-5D) utility score. Also, in sensitivity analyses, we averaged all available values of the outcome and predictor across time, effectively creating one observation per subject, and then a linear regression analysis was applied to those data.

RESULTS: Using the RMM with AE as an anchor, the FKSI-DRS ID generally ranged between 0.74 (AE as a continuous predictor variable) and 1 point (AE as a categorical predictor variable); results of sensitivity analyses were generally consistent. When item “I am bothered by side effects of treatment” score was used as an anchor, FKSI-DRS ID ranged between 1.2 and 1.39 points (depending on the model). When EQ-5D utility score was used as an anchor, the FKSI-DRS ID ranged between 0.63 and 1.0 point.

CONCLUSIONS: Among patients undergoing treatment for mRCC, the evidence suggests that FKSI-DRS between-group differences as low as 1 point may be meaningful.