Breast Relapse of Pediatric B-Cell Acute Lymphoblastic Leukemia After CAR-T Therapy Detected by¹⁸F-FDG PET/CT

Background: B-cell acute lymphoblastic leukemia (B-ALL) is the most common childhood malignancy. Medullary and extramedullary disease relapse is a well-known occurrence in B-ALL pediatric patients treated with standard chemo-immunotherapy and, more recently, with chimeric antigen receptor (CAR)-T cell therapy. ¹⁸F-Fluorodeoxyglucose positron emission tomography/computed tomography (¹⁸F-FDG PET/CT) emerges as a sensitive imaging tool for detecting disease relapse at extra-medullary sites, with only limited literature evidence in the CAR-T therapy setting. Case Report: In a 12-year-old female treated with CAR-T therapy for B-ALL relapse, ¹⁸F-FDG PET/CT scan performed for surveillance, after disease remission, detected a solitary and clinically occult relapse in the breast parenchyma that was histologically confirmed. Conclusion: At our knowledge, this is the first report about a pediatric B-ALL patient with a solitary and occult breast relapse after CAR-T therapy, early discovered by ¹⁸F-FDG PET/CT during disease monitoring.