Somatic DICER1-Mutant Benign Thyroid Nodules in Adults: A Group of Follicular Nodular Disease With Continuous Growth

Abstract Background Germline DICER1 mutations cause familial multinodular goiter (MNG). However, the prevalence of somatic DICER1 mutations in non-MNG benign thyroid nodules and their characteristics remain unknown. Methods Adult-onset thyroid nodules with a pathological diagnosis were genotyped via targeted sequencing. DICER1-mutant nodules were assessed clinically and pathologically. Organoids were established to investigate follicular formation and growth. Transcriptomic analysis was conducted to evaluate transcriptional features, which were validated by immunofluorescence. Results Among 931 adult-onset thyroid nodules, we identified 13 benign thyroid nodules with DICER1 hotspot mutations. The majority harbored a somatic DICER1 hotspot mutation with a somatic DICER1 truncating variant. Clinically, 38.5% of the DICER1-mutant nodules exhibited substantial growth. DICER1-mutant nodules with durations longer than 2 years were substantially enlarged (P=.0448). Pathologically, all DICER1-mutant nodules were defined as thyroid follicular nodular disease (TFND). The TFND nodules with DICER1 mutations grew faster than those with wild-type DICER1. Organoid culture of a DICER1-mutant nodule revealed increased active follicular formation. Compared with the normal thyroid tissues, the DICER1-mutant nodules had comparable thyroid differentiation scores, significantly higher ERK scores (P=.0141) and lower epithelial‒mesenchymal transition scores (P=.0001). Moreover, the expression of genes related to follicular polarity, such as CDH16, SLC5A5, TSHR and TPO, was downregulated in the DICER1-mutant nodules. Conclusions Somatic DICER1 two-hit mutations represent a notable percentage in adult TFND patients, and DICER1-mutant benign thyroid nodules were characterized by continuous growth.