PSYCHOMETRIC VALIDATION OF THE FACT-M QUESTIONNAIRE IN PATIENTS WITH MERKEL CELL CARCINOMA

OBJECTIVES: Assessment of patient-reported outcomes in oncology clinical trials is required to demonstrate treatment benefit from a patient's perspective. No validated tools exist to capture health-related quality of life (HRQoL) in patients with Merkel cell carcinoma (MCC), an ultra-rare skin cancer. The objective of this research was to assess the reliability and validity of the Functional Assessment of Cancer Therapy-Melanoma (FACT-M) questionnaire in patients with MCC. METHODS: Patients with stage IV chemotherapy-refractory MCC completed the FACT-M in a single-arm, open-label, multicenter, international phase 2 trial (NCT02155647). Internal consistency reliability and construct validity of the FACT-M were assessed at baseline and the ability to detect change in tumor size was assessed from baseline to week 7. Minimal important differences (MID) were computed using distribution and anchor-based methods. RESULTS: Baseline assessments were available in 70 patients (mean age: 70 years; 74.3% male). FACT-M domains showed acceptable psychometric properties: high internal consistency reliability (Cronbach's alpha: 0.81 - 0.96) and good convergent validity (correlations above 0.4 were observed for 88% of items of the melanoma surgery scale, 75% of items of the melanoma scale and 100% of items of the other FACT-M domains). Higher scores (better HRQoL) on all FACT-M domains were observed in patients with better functioning (assessed by ECOG performance score), with statistically significant difference in physical well-being score (p=0.0221) supporting clinical validity. Despite the small sample for responsiveness analysis (n=37), the majority of FACT-M scores showed sensitivity to changes in tumor size at week 7 with small to moderate effect sizes. Some evidence of floor/ceiling effects and potential mismatch between items and domains (discriminant validity) was found. MIDs were consistent with previously reported values in the literature for FACT-M domains. CONCLUSIONS: The FACT-M demonstrated acceptable psychometric properties in MCC patients, thus making it a potential candidate for assessing HRQoL in MCC trials.