OBJECTIVES: Fatigue is a major symptom experienced by mCRPC patients. Despite the availability of validated patient-reported outcome measures (PROMs) [e.g., BFI], patient-reported fatigue is not routinely or systematically collected in clinical trials (CTs). The purpose of this analysis was to assess the correlation of individual items from the FACT-P, a PROM used in prostate cancer CTs, and the BFI.

METHODS: Two items from the FACT-P (item 1 [“I have a lack of energy”] and item 7 [“I am forced to spend time in bed”]) were selected as proxies of fatigue. A combined subscale of items 1 and 7 was also created. Pearson correlation coefficients were calculated between items 1 and 7 and combined items 1 and 7 subscale and BFI scores using baseline data from the Phase 3 AFFIRM (NCT00974311) and PREVAIL (NCT01212991) enzalutamide CTs. Correlation effect sizes were presented as absolute values and classified as small (0.1), medium (0.3), large (0.5), or very large (0.7) using Rosenthal’s adjustment (1996) to Cohen’s conventions (1988).

RESULTS: Item 1 showed large to very large correlations with BFI total score (r=0.7123, r=0.6468), fatigue interference (r=0.6720, r=0.5919), and fatigue severity (r=0.7090, r=0.6321) for both AFFIRM and PREVAIL, respectively. Item 7 showed large correlations in AFFIRM for total score and fatigue subscores (range, r=0.5264–0.5777) and medium correlations in PREVAIL (range, r=0.3528–0.4155). The combined subscale showed very large to large correlations with BFI total score (r=0.7522, r=0.6717), fatigue interference (r=0.7241, r=0.6275), and fatigue severity (r=0.7208, r=0.6346) for AFFIRM and PREVAIL.

CONCLUSIONS: Item 1 and the combined subscale demonstrate strong correlations between the FACT-P and BFI in mCRPC patients. Using the single item “I have a lack of energy” or the combined subscale may help provide additional context when trying to understand and interpret the patient experience regarding fatigue.

FUNDING: Astellas Pharma Inc.; Pfizer Inc.

EDITORIAL: Complete HealthVizion