Prevalence and Spectrum of <i>DICER1</i> Mutations in Adult-onset Thyroid Nodules with Indeterminate Cytology

Abstract Context DICER1 mutations are found in multinodular goiter and differentiated thyroid carcinoma in children, and can be a manifestation of DICER1 syndrome, but the prevalence of DICER1 mutations and their significance in adult-onset thyroid nodules is unknown. Objective Determine (1) the prevalence of DICER1 hotspot mutations in thyroid nodules; (2) the frequency of a second DICER1 pathogenic variant in thyroid nodules with DICER1 hotspot mutations; (3) the prevalence of other thyroid cancer driver mutations in thyroid nodules with and without DICER1 hotspot mutations. Methods Population-based study of 14 993 consecutive fine needle aspiration biopsies of thyroid nodules evaluated by ThyroSeq v3. From 214 DICER1 hotspot–positive cases, we selected 61, matched to DICER1 hotspot–negative nodules. We performed full sequencing of all exons and exon–intron boundaries of DICER1. Setting Commercial and university-based laboratories in the United States and Canada. Results Among 14 993 thyroid nodules, 214 (1.4%) revealed a DICER1 hotspot mutation. A second pathogenic/likely pathogenic variant in DICER1 was found in 45/59 (76%) DICER1 hotspot–positive nodules studied while no other DICER1 variant was identified in the DICER1 hotspot–negative group by full DICER1 sequencing. Other alterations in thyroid-related genes were significantly more frequent in DICER1 hotspot–negative nodules (32/61) than in DICER1 hotspot-–positive nodules (4/59) (P &lt; .0001). Conclusion DICER1 alterations occur in a proportion of adult thyroid nodules and appear mutually exclusive with alterations in other thyroid cancer–related genes. DICER1 hotspot mutations occur with a second hit in most cases and could suggest occult DICER1 syndrome in adults with thyroid nodules.