Reversing “Flip-Flop” Phenomenon of 131I and Glucose Avidity in RET-Fusion Positive Radioiodine-Refractory Thyroid Cancer Lesions After Treatment of Pralsetinib
Hung-Pin Chan, I-Feng Chen, Fu-Ren Tsai, Chun-Hao Kao, Daniel Hueng-Yuan Shen
Abstract
ABSTRACT: A 61-year-old man presented with papillary thyroid cancer in radioiodine-refractory status after high-activity 131 I treatments following thyroidectomy. FDG-avid neck and pulmonary metastases but without 131 I-uptake were detected. CCDC6-RET fusion was identified from the tumor lesion. He was treated with pralsetinib, a RET inhibitor, followed by another high-activity 131 I therapy. Posttherapeutic scan displayed restoration of 131 I avidity at those lesions only shown on previous FDG PET/CT. Reduced FDG avidity of those lesions and decreased serum antithyroglobulin antibody titer were also noticed. This case illustrated successfully reinduced 131 I avidity in papillary thyroid cancer through redifferentiation with target therapy to suppress tumor RET overexpression.