Comprehensive characterization of DICER1 mutations and two hit tumorigenesis mechanisms in follicular thyroid carcinoma using multi-omics analysis

Background: DICER1 is an essential RNase III enzyme for microRNA (miRNA) processing. Germline loss-of-function (LoF) variants cause DICER1 syndrome and predispose younger individuals to tumors including follicular thyroid carcinoma (FTC). Somatic RNase IIIb hotspot mutations are characteristic, but how germline LoF, somatic hits, and tissue-specific regulatory networks drive FTC is not fully understood. Methods: We analyzed DICER1-mutant FTC (n=20) using whole-exome sequencing, miRNA-seq, RNA-seq, and proteomics, and compared them with wild-type tumors (wt-T, n=61). Tumors were classified as syndrome-associated (syn-T, n=7) or sporadic (spo-T, n=13). Integrative analyses included allelic imbalance, pathway enrichment, and network modeling (WGCNA). Results: Clinically, spo-T patients were significantly younger than wt-T, indicating an age-specific window for DICER1-driven FTC. Most tumors showed biallelic disruption through RNase IIIb hotspot mutations with secondary LoF events, and allelic imbalance confirmed two-hit inactivation even when only one mutation was detected.In syndrome-normal tissues, substantial mRNA dysregulation occurred without miRNA changes, suggesting DICER1 haploinsufficiency acts independently of global miRNA loss.In DICER1-mutant tumors, cell-cycle, mTOR, and Wnt pathways were strongly upregulated, whereas immune programs were broadly suppressed. The thyroid stem-cell marker REXO1 was specifically elevated, indicating a stem-like phenotype. Network analysis highlighted CTNNB1 and let-7i as key regulators of the DICER1 transcriptional program. Although DICER1- and RAS-mutant FTCs shared some downstream signaling modules, DICER1-mutant tumors retained a distinct expression identity. WGCNA identified a DICER1-specific cell-cycle module and a partially shared DICER1-RAS Wnt/MAPK module. Conclusion: DICER1 functions as a distinct oncogenic driver in FTC, following a biallelic inactivation model and producing unique proliferative, immune-suppressed, and stem-like transcriptional states. These findings refine the mechanism of DICER1-associated thyroid tumorigenesis and suggest potential lineage-specific therapeutic targets.