BACKGROUND Molecular characterization in pediatric papillary thyroid cancer (PTC), distinct from adult PTC, is important for developing molecularly targeted therapies for progressive radioiodine-refractory (131I-refractory) PTC.METHODS PTC samples from 106 pediatric patients (age range: 4.3–19.8 years; n = 84 girls, n = 22 boys) who were admitted to SNUH (January 1983–March 2020) were available for genomic profiling. Previous transcriptomic data from 125 adult PTC samples were used for comparison.RESULTS We identified genetic drivers in 80 tumors: 31 with fusion oncogenes (RET in 21 patients, ALK in 6 patients, and NTRK1/3 in 4 patients); 47 with point mutations (BRAFV600E in 41 patients, TERTC228T in 2 patients [1 of whom had a coexisting BRAFV600E], and DICER1 variants in 5 patients); and 2 with amplifications. Fusion oncogene PTCs, which are predominantly detected in younger patients, were at a more advanced stage and showed more recurrent or persistent disease compared with BRAFV600E PTCs, which are detected mostly in adolescents. Pediatric fusion PTCs (in patients <10 years of age) had lower expression of thyroid differentiation genes, including SLC5A5, than did adult fusion PTCs. Two girls with progressive 131I-refractory lung metastases harboring a TPR-NTRK1 or CCDC6-RET fusion oncogene received fusion-targeted therapy; larotrectinib and selpercatinib decreased the size of the tumor and restored 125I radioiodine uptake. The girl with the CCDC6-RET fusion oncogene received 131I therapy combined with selpercatinib, resulting in a tumor response. In vitro 125I uptake and 131I clonogenic assays showed that larotrectinib inhibited tumor growth and restored radioiodine avidity.CONCLUSIONS In pediatric patients with fusion oncogene PTC who have 131I-refractory advanced disease, selective fusion-directed therapy may restore radioiodine avidity and lead to a dramatic tumor response, underscoring the importance of molecular testing in pediatric patients with PTC.FUNDING The Ministry of Science, ICT and Future Planning (NRF-2016R1A2B4012417 and 2019R1A2C2084332); the Korean Ministry of Health and Welfare (H14C1277); the Ministry of Education (2020R1A6A1A03047972); and the SNUH Research Fund (04-2015-0830).TRIAL REGISTRATION Two patients received fusion-targeted therapy with larotrectinib (NCT02576431; NAVIGATE) or selpercatinib (LOXO-RET-18018).
Young Ah Lee, Hyunjung Lee, Sun-Wha Im, Young Shin Song, Do-Youn Oh, Hyoung Jin Kang, Jae-Kyung Won, Kyeong Cheon Jung, Dohee Kwon, Eun-Jae Chung, J. Hun Hah, Jin Chul Paeng, Ji-hoon Kim, Jaeyong Choi, Ok-Hee Kim, Ji Min Oh, Byeong-Cheol Ahn, Lori J. Wirth, Choong Ho Shin, Jong-Il Kim, Young Joo Park