Abstract: We evaluated the psychometric properties of the Spanish version of the European Organization for Research and Treatment of Multiple Myeloma (MM) specific quality-of-life (QoL) questionnaire module (QLQ-MY20) in relapsed/refractory MM (RRMM) patients. This was an observational, cross-sectional, multicenter study using EORTC QLQ-C30 and QLQ-MY20 in RRMM patients (ClinicalTrials.gov ID NCT03188536). We assessed the non-response rate, ceiling/floor effects, internal consistency, test-retest reliability, and validity. The study included 276 patients (53.3% males, mean [SD] age of 67.4 [10.5] years). The EORTC QLQ-MY20 showed a low non-response rate, very low ceiling and floor effects, and good internal consistency. The test-retest reliability assessment revealed good temporary stability, the construct validity analysis stated four main factors similar to the ones of the original version, and the criterion validity assessment showed no differences between groups. In conclusion, the Spanish version of EORTC QLQ-MY20 is a reliable and valid tool for assessing QoL in RRMM patients
