- PURPOSE: Using health-related quality-of-life measures for patient management requires knowing what changes in scores require clinical attention. We estimated changes on the European Organization for Research and Treatment of Cancer Quality-of-Life-Questionnaire-Core-30 (EORTC-QLQ-C30), representing important changes by comparing to patient-reported changes in supportive care needs. METHODS: This secondary analysis used data from 193 newly diagnosed cancer patients (63 % breast, 37 % colorectal; mean age 60 years; 20 % male) from 28 Canadian surgical practices. Participants completed the Supportive Care Needs Survey-Short Form-34 (SCNS-SF34) and EORTC-QLQ-C30 at baseline, 3, and 8 weeks. We calculated mean changes in EORTC-QLQ-C30 scores associated with improvement, worsening, and no change in supportive care needs based on the SCNS-SF34. Mean changes in the EORTC-QLQ-C30 scores associated with the SCNS-SF34 improved and worsened categories were used to estimate clinically important changes, and the 'no change' category to estimate insignificant changes. RESULTS: EORTC-QLQ-C30 score changes ranged from 6 to 32 points for patients reporting improved supportive care needs; statistically significant changes were 10-32 points. EORTC-QLQ-C30 score changes ranged from 21-point worsening to 21-point improvement for patients reporting worsening supportive care needs; statistically significant changes were 9-21 points in the hypothesized direction and a 21-point statistically significant change in the opposite direction. EORTC-QLQ-C30 score changes ranged from a 1-point worsening to 16-point improvement for patients reporting stable supportive care needs. CONCLUSION: These data suggest 10-point EORTC-QLQ-C30 score changes represent changes in supportive care needs. When using the EORTC-QLQ-C30 in clinical practice, scores changing ≥10 points should be highlighted for clinical attention.