Introduction
- Thyroid nodules (TN) are rare in children and carry a higher risk of malignancy (~25%) compared to adults (~5-10%).1
- The Afirma GSC is an exome-enriched RNAseq assay that sequences over 21,000 gene transcripts, allowing for the detection of gene expression, sequence variants, gene fusions, and gene expression pathways.2
- This study aimed to assess molecular differences related to malignancy in TN from patients < and ≥ 21 yrs.
Methods
Cytologic and molecular differences were assessed in 177,227 TN samples tested by the Afirma Genomic Sequencing Classifier (GSC) through 12/2022.
Genome-wide differential gene expression (DGE), mutation profiles, and expression signatures were compared between < and ≥ 21 yrs patients using Fisher's exact and Wilcoxon rank tests.
Results
There were 1,583 < 21 yrs patients (median age 18.9 yrs (IQR 17.1-20.0; 80.3% female)) and 175,644 ≥ 21 yrs patients (median age 59.3 yrs (IQR 46.0-69.0; 77.5% female)). When associating age group to Bethesda group, more Bethesda V&VI were found in the young patients (< 21 yr) compared to older patients (12.3% vs 4.4%, p value < 2e-16). Within the young group, there was no significant enrichment of Bethesda V/VI in either gender (11.2% for male, 12.5% for female, p=0.6). Among cytologically indeterminate TN (ITN), 56% of < 21 yrs patients were GSC-(S)uspicious compared to 31% of ≥ 21 yrs (p<0.001). (Table 1a-c).
ITN GSC-S in < 21 yrs had overall more variants (44.8% vs 37%) and relative differences in certain molecular variants compared to older patients including: A higher rate of BRAFV600E, DICER1, and TSHR. There were less frequent HRAS and SPOP variants (Table 2).
Amongst DICER1 variants, those associated with poorly differentiated thyroid histology (codons 1709/1705/1813) were more frequently found in the < 21 yrs group (7.2% vs 0.7%, p<0.001).
ITN GSC-S in < 21 yrs had more frequent fusions (13.6% vs 5.7%, p<0.001), particularly ETV6::NTRK3 (5%) and CCDC6::RET (2.7%), as well as ALK fusions (1%) (Table 3).
Transcriptionally, < 21 yrs TN expressed higher ERK and MYC activity and cell cycle-related pathways (adjusted p value < 0.05). DGE identified overexpression of genes associated with cell cycle-related gene sets (e.g. KEGG cell cycle, G2-M). Among the subset of thyroid nodules with NTRK, RET, or ALK fusions, < 21 yrs was associated with higher expression of angiogenesis, epithelial-mesenchymal transition, and cell cycle gene sets (adjusted p value < 0.05) (Figure 1).
BRAF-RAS score (a marker of how BRAF-like a tumor is) was not different between the age groups.
Conclusion
- Thyroid tumors from younger patients are unique by having more than double the prevalence of targetable fusions (NTRK and RET), high-risk somatic DICER1 variants, and higher expression of cell cycle-related gene sets.
- Future investigation of these molecular differences may provide insights into the distinct clinical presentations of thyroid cancer between younger patients and adults.