Understanding the major factors affecting response shift effects on health-related quality of life: what the then-test measures in a longitudinal prostate cancer registry

BACKGROUND: Localized prostate cancer (PCa) treatments provide high survival rates, with patients often surviving a decade or longer after treatment. Therefore, treatment options are progressively based on quality of life. The objective of this research was to investigate magnitude of response shift (RS) in health-related quality of life (HRQOL) responses in men with clinically localized PCa using a generic questionnaire and a disease-specific questionnaire in an observational longitudinal patient registry study.

PATIENTS AND METHODS: A cohort study was conducted using the Cancer of the Prostate Strategic Urologic Research Endeavor (CaPSURE) database. Patients were annually surveyed using the Medical Outcomes Study Questionnaire Short Form 36 (SF-36) and the UCLA Prostate Cancer Index (PCI) HRQOL measures. A total of 3161 active patients were eligible for a one-off supplemental study asking retrospective HRQOL scores (then-test). We calculated RS, observed change, and RS adjusted change. Statistical difference was determined by t test.

RESULTS: Patients consistently reported higher recalled pretreatment HRQOL compared to baseline scores for SF-36 and PCI, confirming the existence of a RS (P < .05). On average, PCI demonstrated larger RS by a factor of 2 than SF-36. More specific, RS was greater especially in SF-36 physical domains compared to mental health items. PCI measured PCa-specific physical adverse effects only. Patients whose cancer had recurred reported slightly lower SF-36 RS than those whose cancer had not recurred.

CONCLUSION: RS occurrence was measured in both the disease-specific questionnaire and the generic HRQOL questionnaire, demonstrating continued low health and symptom scores after RS adjustment. Therefore, health professionals should adjust for this phenomenon when assessing patient's HRQOL treatment responses, and clinicians should address their continued sexual and urinary functional loss.