Meaningful differences and validity for the NCCN/FACT-P Symptom Index: An analysis of the ALSYMPCA data

Abstract

Background: The Functional Assessment of Cancer Therapy–Prostate (FACT-P) and the National Comprehensive Cancer Network/Functional Assessment of Cancer Therapy–Prostate Symptom Index-17 (NFPSI-17) are 2 commonly used measures for patient-reported outcomes in prostate cancer trials. Their use may be enhanced by a better understanding of how change scores on the measures should be interpreted. Methods: Using data from the phase 3 Alpharadin in Symptomatic Prostate Cancer Patients trial, this study estimated important change scores on the FACT-P and the NFPSI-17 via a combination of distribution- and anchor-based methods. These data were also used to establish evidence for the validity of the NFPSI-17. Results: The available data suggested the following important difference ranges: 2 to 4 points for the Prostate Cancer Subscale, 5.5 to 8.5 points for the Trial Outcome Index, 1 to 1.5 points for the 3-item Pain Scale, 1 to 2 points for the 4-item Pain Scale, 4 to 6 points for the NFPSI-17, 2 to 3.5 points for NFPSI–Disease-Related Symptoms–Physical, 0.5 points for NFPSI–Disease-Related Symptoms–Emotional, 1 to 1.5 points for NFPSI–Treatment Side Effects, and 0.5 to 1 point for NFPSI–Function/Well-Being. The internal consistency reliability of the NFPSI-17 and most of its subscales was good to excellent (>.70). Significant support was also found for the known groups validity of the NFPSI-17 (and most of its subscales) on the basis of the Eastern Cooperative Oncology Group performance status, the total alkaline phosphatase, the presence of a skeletal-related event during treatment, and the prostate-specific antigen response before the end of treatment. Conclusions: The secondary analysis supports the continued use of the FACT-P, the NFPSI-17, and its related subscales in future research on the quality of life of patients with symptomatic castration-resistant prostate cancer with bone metastases.