Minimal Clinically Important Difference of the Multidimensional Fatigue Symptom Inventory-Short Form (MFSI-SF) for Fatigue Worsening in Asian Breast Cancer Patients.

CONTEXT: The minimal clinically important difference (MCID) of the Multidimensional Fatigue Symptom Inventory-Short Form (MFSI-SF), a questionnaire that measures cancer-related fatigue, has not been established in patients with cancer.

OBJECTIVES: This study aims to determine the MCID of the MFSI-SF.

METHODS: Breast cancer patients completed the MFSI-SF and the European Organization for Research and Treatment of Cancer Quality of Life Questionnaire-Core 30 (EORTC-QLQ-C30) before chemotherapy and at least three weeks later. The EORTC-QLQ-C30 fatigue scale (EORTC-FA) was used as an anchor, and a receiver operating characteristic (ROC) curve was also used to identify the optimal MCID cut-off for fatigue deterioration. A distribution-based approach used one-third of the SD, half of the SD, and one SEM of the total MFSI-SF score to determine the MCID.

RESULTS: A total of 201 patients were analyzed. Change scores of the MFSI-SF and EORTC-FA were moderately correlated (r = 0.47, P < 0.001). The EORTC-FA-anchored MCID was 8.69 points (95% CI: 4.03-13.34). The MCID attained from the ROC curve method was 4.50 points (sensitivity: 68.8%; specificity: 64.1%). For the distribution-based approach, the MCIDs corresponding to one-third of the SD, half of the SD, and one SEM were 5.39, 8.99, and 10.79 points, respectively.

CONCLUSION: The MCID of the MFSI-SF identified by all approaches ranged from 4.50 to 10.79 points. The MCID can be used to interpret the clinical significance of fatigue deterioration in patients with breast cancer and to determine sample sizes for future clinical trials.