Minimal clinically important difference (MCID) for the functional assessment of cancer therapy: Cognitive function (FACT-Cog) in breast cancer patients.

6589 Background: Establishing the Minimal Clinically Important Difference (MCID) is essential for interpreting the clinical relevance of patient reported outcomes. This is the first study to date to determine the MCID of FACT-Cog, a 37-item validated subjective neuropsychological instrument designed to evaluate cancer patients’ perceived cognitive deterioration on their quality of life. Methods: This prospective, observational study involved 220 breast cancer patients who have completed FACT-Cog and EORTC-QLQ-C30 at two time points: baseline and at least 3 months following chemotherapy. The MCID was computed using 3 approaches: 1) an anchor-based approach utilized the validated EORTC-QLQ-C30-Cognitive Functioning scale (CF) as the anchor for patients who showed a minimal deterioration on the CF (defined as a one-step deterioration on the CF scale); 2) a Receiver Operating Characteristic (ROC) curve was used to identify an optimal MCID cut-off point for deterioration; 3) a distribution-based approach utili...