Estimating Clinically Meaningful Changes for the Functional Assessment of Cancer Therapy—Prostate: Results from a Clinical Trial of Patients with Metastatic Hormone-Refractory Prostate Cancer

Abstract

Objective To determine clinically meaningful changes (CMCs) for the Functional Assessment of Cancer Therapy–Prostate (FACT–P). Methods We obtained data from a Phase III trial of atrasentan in metastatic hormone-refractory prostate cancer patients (n = 809). We determined anchor-based differences using Karnofsky Performance Status (KPS), bone alkaline phosphatase (BAP), hemoglobin, time to disease progression (TTP), adverse events (AE), and survival. One-third and one-half standard deviation and standard error of measurement (SEM) were used as distribution-based criteria for CMCs. Comparison across baseline FACT–P domains and derived scales [FACT–P total score, Trial Outcome Index (TOI) score, prostate cancer subscale (PCS) score, pain-related score, and FACT Advanced Prostate Symptom Index (FAPSI)] were conducted for KPS, BAP, and hemoglobin using Student's t tests. Twelve-week change scores were compared for TTP, AE, and survival using ANCOVA. Results CMCs were estimated as 6 to 10 for FACT–P total score, 5 to 9 for FACT–P TOI score, 2 to 3 for FACT–P PCS, 1 to 2 for the 4 PCS pain-related questions, and 2 to 3 for FAPSI. CMCs were also estimated using distribution-based criteria. Kappa statistics were computed to determine the degree of correspondence between the recommended guideline of 1.0 SEM and empirically derived standards. Most of the kappas for health-related quality of life domains and SEM standards had “substantial” to “almost perfect” concordance. Conclusions The significant relationship between clinical and quality of life data provides support for the use of CMCs to increase interpretability of FACT–P scores.