The challenge of measuring intra-individual change in fatigue during cancer treatment.

Purpose: To evaluate how well three different patient-reported outcomes (PROs) measure individual change.

Methods: Two hundred and fourteen patients (from two sites) initiating first or new chemotherapy for any stage of breast or gastrointestinal cancer participated. The 13-item FACIT Fatigue scale, a 7-item PROMIS Fatigue Short Form (PROMIS 7a), and the PROMIS Fatigue computer adaptive test (CAT) were administered monthly online for 6 months.