NTRK and RET fusion-directed therapy in pediatric thyroid cancer yields a tumor response and radioiodine uptake

Abstract

BACKGROUNDMolecular 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.METHODSPTC 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.RESULTSWe 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.CONCLUSIONSIn 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.FUNDINGThe 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 REGISTRATIONTwo patients received fusion-targeted therapy with larotrectinib (NCT02576431; NAVIGATE) or selpercatinib (LOXO-RET-18018).

Keywords: Cancer; Endocrinology; Oncogenes; Oncology; Thyroid disease.

Conflict of interest statement

Conflict of interest: The authors have declared that no conflict of interest exists.

Figures

Figure 1. Flow diagram describing comprehensive genomic profiling of pediatric PTC samples.

Tumor tissue samples (n = 106) from pediatric patients with PTC (n = 84 girls, n = 22 boys; median age: 14.3 years; range: 4.3–19.8 years) were analyzed to profile genetic alterations using WGS, targeted sequencing, mRNA sequencing, direct sequencing, FISH, and/or IHC depending on the availability of each tissue. FTC, follicular thyroid cancer; MTC, medullary thyroid cancer; PDTC, poorly differentiated thyroid cancer.

Figure 2. Age-associated genetic profiles of pediatric PTCs and comparison of the clinicopathological presentation and disease outcomes between fusion oncogene and BRAFV600E PTCs.

(A–D) Age-associated proportions of fusion oncogenes, point mutations, and genetic drivers among the pediatric patients in this study (A and B; patients aged <10 years, n = 14; 10–14 years; n = 40, and 15–19 years, n = 52) and a pooled analysis of 1704 patients under 23 years of age (C and D; patients aged <10 years, n = 68 and patients aged 10–22 years, n = 468, plus other patients without detailed age information). Comparison of the clinicopathological presentation (E) and disease outcomes (F) among the 3 pediatric groups: fusion PTCs in patients <10 years of age (n = 13), fusion PTCs in patients 10–19 years of age (n = 18), and BRAFV600E PTCs in all patients 10–19 years of age (n = 41). Comparison of the clinicopathological presentation (G) and disease outcomes (H) between the pediatric fusion (n = 31) and adult fusion (n = 12) groups, and between the pediatric BRAFV600E (n = 41) and adult BRAFV600E (n = 68) groups. Categorical variables were compared between the 2 groups using the χ2 or Fisher’s exact test, whereas the χ2 test for trend or logistic regression was used for comparisons among the 3 groups (*P < 0.05, **P < 0.01, and ***P < 0.001). (I) Recurrence-free survival was compared among these 4 groups with reference to the pediatric fusion group. Recurrence-free survival plots were constructed using the Kaplan-Meier method, and groups were compared using the Cox proportional hazards model. The HRs, 95% CIs, and P values are reported in the figure. F/U, follow-up; meta, metastasis.

Figure 3. Comparison of expression signatures between pediatric and adult PTCs.

(A and B) Results of K-means clustering (obtained via principal component analysis). (A) Comparison between 12 pediatric PTCs (9 fusion oncogenes and 3 BRAFV600E PTCs) and 125 adult PTCs, including BRAF-like, RAS-like, and non-BRAF–non-RAS (NBNR). (B) Comparison between pediatric (n = 9) and adult (n = 12) PTCs with fusion oncogenes. The patients’ ages and mutation types are represented by shapes and colors, respectively. (C) Box plots (left) show the ERK score, TDS, and SLC5A5 (NIS) analysis results. Scatterplot (right) shows the results of the TDS and ERK score analysis. (D) Heatmap shows the expression levels of 16 TDS genes associated with thyroid function and metabolism. Comparison of TDS gene expression levels between the pediatric (ped) and adult fusion groups and between the pediatric and adult BRAFV600E groups using fresh-frozen tissue samples. cPTC, classic variant PTC; DSV-PTC, diffuse sclerosing variant PTC; FVPTC, follicular variant PTC; TCV, tall cell variant PTC. (E) Comparison of TDS genes between pediatric PTCs and normal thyroid tissues based on an analysis of FFPE samples. Two young girls (P1 and P8) with progressive 131I-refractory lung metastasis had low expression of SCL5A5 in their tumor tissues.

Figure 4. Selective fusion-targeted therapy decreased the tumor size and restored radioiodine uptake in 131I-refractory progressive metastatic pediatric PTCs.

Radioactive iodine (RAI) WBS and single-photon emission computed tomography (SPECT) CT scans of a 4.3-year-old girl with TPR-NTRK1 fusion–positive PTC (A and B) and a 7.4-year-old girl with CCDC6-RET fusion–positive PTC (C and D). (A) The post-treatment WBS showed remnant thyroid uptake only. Radioiodine uptake was restored in the cervical LN and lung lesions after 12 weeks of larotrectinib therapy. (B) A CT scan revealed a dramatic improvement in the LN and lung target lesions (decreased to 35% of baseline) after 4 weeks. The patient achieved complete remission after 21 months and remained responsive, with no dose-limiting toxicity seen during 41 months of larotrectinib therapy. (C) The post-treatment WBS revealed minimal uptake of radioiodine in the lungs. Radioiodine uptake was restored in the entire lung field after 5 months of selpercatinib treatment (Tx). The addition of 131I (60 mCi) 13 months after starting selpercatinib treatment resulted in remarkable radioiodine uptake in the lung field. (D) Lung lesions were markedly improved according to a chest radiograph done 10 days later and decreased to 42.9% of baseline on a CT scan after 4 weeks. The patient achieved partial remission after 4 weeks and remained responsive, with no dose-limiting toxicity seen during 29 months of selpercatinib therapy.

Figure 5. In vitro effects of larotrectinib on radioiodine uptake capacity and cell growth.

(A) Baseline 125I uptake decreased in NthyTPR-NTRK cells compared with NthyWT cells but was restored by larotrectinib treatment mediated by the NIS; this was demonstrated by blocking the effects with KCIO4. Expression of the NIS at the mRNA (B) and protein (C) levels tended to increase in NthyTPR-NTRK cells with larotrectinib (50 μM) treatment. (D) The colony-forming ability of NthyTPR-NTRK cells did not change after 131I therapy alone but decreased after larotrectinib treatment, and then further decreased after combined 131I and larotrectinib therapy. *P < 0.05, **P < 0.01, and ***P < 0.001, by Student’s t test or 1-way ANOVA with Bonferroni’s multiple-comparison test. All data represent the mean ± standard deviation. LAR, larotrectinib (50 μM).