Validation of the 7‐Item Quality of Life Disease‐Specific Impact Scale in Patients Undergoing Radical Cystectomy for Bladder Cancer: A Cross‐Sectional Study

OBJECTIVES: To validate, for the first time in patients with bladder cancer who underwent radical cystectomy, the recently developed 7-item Quality of Life Disease-specific Impact Scale (QDIS-7), a brief, unidimensional instrument designed for cross-condition comparisons. METHODS: In this cross-sectional study conducted at 24 facilities, patients aged ≥ 20 years who were 3 months post-radical cystectomy for bladder cancer completed self-reported questionnaires. The enrollment period was from January 2020 to October 2022. Quality of life measures included the QDIS-7, the Bladder Cancer Index (BCI), and the Body Image Scale (BIS). Confirmatory factor analysis was performed to test the hypothesized one-factor structure of the QDIS-7. Internal consistency reliability was assessed using Cronbach's alpha coefficient. Criterion-based validity was evaluated using Spearman's correlation coefficients (ρ) between the QDIS-7 scores and the BCI bother subdomains and BIS scores. RESULTS: In total, 205 patients (median age, 71 years; 78.5% male) were included. The QDIS-7 score showed no floor or ceiling effects. Confirmatory factor analysis supported the one-factor model (factor loadings, 0.71-0.94). Internal consistency reliability was high (Cronbach's alpha, 0.94). The QDIS-7 score showed moderate correlations with the BIS and the BCI urinary and bowel bother subdomain scores (ρ = 0.654, -0.560, and -0.475, respectively). CONCLUSIONS: The QDIS-7 effectively captured urinary and bowel symptom burden and body image impairment in patients undergoing radical cystectomy for bladder cancer. Its brevity, strong psychometric properties, and capacity for comparisons across conditions support its use in patient-centered research. TRAIL REGISTRATION: UMIN-CTR (UMIN000039538).