OBJECTIVES : To ensure reliable, valid assessments of patients’ Health-Related Quality of Life (HRQOL), it is important to use psychometrically robust instruments. In the context of rare diseases, such as metastatic MCC (mMCC), disease-specific instruments are often not available, so instruments from related diseases are used. Previously, the psychometric performance of FACT-M was documented in a cohort of patients with mMCC whose disease progressed after chemotherapy. This study aims to confirm the psychometric performance of FACT-M in patients with mMCC who were either treatment naive or had previously received chemotherapy.

METHODS : Based on a previously published qualitative analysis, it was confirmed that patients with mMCC, whether treatment naive or previously treated, had similar experiences and concepts associated with their disease. Patient-report outcomes (PRO) data were pooled (n=173) from the single-arm, phase 2 JAVELIN Merkel 200 trial (NCT02155647) from part A (previously treated, n=70) and part B (treatment naive, n=103). Cronbach α was used to assess internal consistency reliability. Convergent validity was assessed using correlations with EQ-5D items. Known-groups validity was explored using ECOG performance status (PS) 0 vs 1.

RESULTS : Cronbach α for all FACT-M scales was excellent, ranging between 0.80 (emotional well-being) and 0.95 (FACT-M total score). As expected, FACT-M subscale scores generally correlated highest with EQ-5D items that measured similar constructs, suggesting good concurrent validity. Known-groups validity analyses showed that the FACT-M differentiated well between ECOG PS 0 and 1. For all subscales, patients with ECOG PS=1 had worse scores compared to ECOG PS=0, with p<0.05 except for social well-being.

CONCLUSIONS : In the context of rare diseases, which often have limited data available for instrument validation, this analysis confirmed the previously established psychometric performance of FACT-M in patients with mMCC regardless of prior treatment status, reaffirming its suitability for this patient population.