Background <p>Bladder cancer significantly impacts patients’ quality of life, making patient-reported outcomes (PROs) a crucial component of clinical evaluation and care. However, patients’ internal standards, values, or conceptualizations may change over time due to diagnosis or treatment experiences—a phenomenon known as response shift —which can threaten the validity of longitudinal PRO assessments and remains underexplored in this population. This study aims to explore response shift in the evaluation of PROs among bladder cancer patients and to identify its underlying mechanisms, using a phenomenological qualitative design.</p> Methods <p>Semi-structured interviews were conducted between December 2023 and October 2024 in the urological wards of a tertiary-level hospital in China. Purposive sampling was used to recruit 14 patients with bladder cancer. Colaizzi’s phenomenological analysis method was used to analyze the data.</p> Results <p>Three themes were identified as relevant to response shift effects on PROs of bladder cancer patients: multidimensional preoperative and postoperative stressors as triggering antecedents of response shift; cognitive adjustment strategies constituting response shift mechanisms; two divergent adaptive outcomes after exposure to bladder cancer stress.</p> Conclusions <p>Response shift was observed in PROs three months after surgery for bladder cancer. Understanding the mechanisms behind response shift can help healthcare professionals interpret patient feedback more accurately and optimize personalized care strategies.</p>