Reliability, validity, and change thresholds of the NCCN/FACT Bladder Symptom Index (NFBlSI‐18) in patients with advanced urothelial cancer

Background The NCCN/FACT Bladder Symptom Index‐18 (NFBlSI‐18) is a bladder cancer–specific instrument. We aimed to psychometrically evaluate the reliability and validity of NFBlSI‐18 and estimate change thresholds for total, disease‐related symptoms‐physical (DRS‐P), DRS‐emotional (DRS‐E), and function/well‐being (F/WB) scales in patients with locally advanced/metastatic urothelial cancer (la/mUC). Methods JAVELIN Bladder 100 trial data were analyzed. Anchors to evaluate validity included: 5‐level EuroQoL‐5D utility index (EQ‐5D‐5L UI), visual analog scale (VAS), Eastern Cooperative Oncology Group (ECOG) performance status, and number of symptoms. Responsiveness to change was tested by anchoring to time to tumor progression (TTP), best overall response (BOR), and differences in means between ECOG categories to estimate meaningful between‐group differences. Meaningful within‐group change thresholds were estimated using receiver operating characteristic curve analysis, anchoring to change in EQ‐5D‐5L UI. Significant within‐individual patient change thresholds were estimated with reliable and likely change indexes. Results Correlations with EQ‐5D‐5L UI and VAS ranged from 0.53 to 0.73. Standardized effect sizes were >0.20. Compared with patients with TTP of ≥6 months, patients with TTP of >0–2 and 3–5 months had larger declines; results for BOR were similar. Thresholds (points) for meaningful between‐group differences were: total, 6–11; DRS‐P, 3–6; and DRS‐E and F/WB, 1. Thresholds (points) for meaningful within‐group worsening were: total, 4; and DRS‐P, 3, and for significant individual change they were: total, 3–9; DRS‐P, 2–6; DRS‐E, 1–3; and F/WB, 2–4. Conclusions NFBlSI‐18 exhibited evidence of reliability, validity, and responsiveness to assess quality of life in studies of la/mUC, and change thresholds are established for future studies. Plain Language Summary The NCCN/FACT Bladder Symptom Index‐18 (NFBlSI‐18) is a questionnaire used to assess quality of life for people with advanced bladder cancer. People with advanced bladder cancer who took part in the JAVELIN Bladder 100 study completed the NFBlSI‐18 when they joined the study and after each treatment with avelumab maintenance or best supportive care. This study showed that NFBlSI‐18 is suitable for capturing bladder cancer symptoms and is able to detect important changes in a person’s quality of life over time. This study also provides thresholds for changes in NFBlSI‐18 scores, which will be usefu