A Mixed-Methods Study to Better Measure Patient-Reported Pain and Fatigue in Soft Tissue Sarcoma

Introduction: Pain and fatigue are commonly reported by patients with soft tissue sarcoma (STS) as distressing symptoms, yet no patient-reported outcome (PRO) measures have been validated or developed specifically for STS. This study aimed to develop novel PRO scales using existing item banks to measure pain and fatigue in STS. Methods: A three-stage mixed-methods approach was used. Stage 1: a literature review examined the development and validation of the European Organization for Research and Treatment of Cancer (EORTC) library, Patient-Reported Outcomes Measurement Information System (PROMIS) pain/fatigue item banks, Functional Assessment of Cancer Therapy-General, and FACIT-Fatigue. Conceptual models were developed for pain and fatigue. Stage 2: semi-structured interviews were conducted with clinical experts (n = 3) and STS patients (n = 28) to ensure conceptual coverage and cognitively debrief the selected PRO items. Stage 3: exploratory Rasch measurement theory (RMT) analyses were performed to examine the measurement properties of the proposed scales. Results: Stage 1: The conceptual model for fatigue was organized into two overarching domains: fatigability and fatigue, further split into two subdomains: symptoms and impact. The conceptual model for pain had one overarching domain split into two subdomains: descriptors and impact. Pain (n = 56) and fatigue (n = 40) items were selected from the EORTC item library. Stage 2: qualitative findings ensured conceptual coverage, provided insight into the relevance and comprehension of the items, and informed subsequent item reduction. Stage 3: The total item number was reduced to 43 (pain n = 18, fatigue n = 25). Exploratory RMT analyses supported the final scales' psychometric properties. Conclusions: This mixed-methods research generated important information on the experience of pain and fatigue in specific subtypes of STS. Five novel PRO scales have been developed through careful item selection in consultation with experts and supported by qualitative and quantitative evidence. These scales may be of value to future clinical trials for STS.