['Nontoxic multinodular goiter (MNG) occurs frequently, but its genetic etiology is not well established. Familial MNG and MNG occurring with ovarian Sertoli-Leydig cell tumor are associated with germline DICER1 mutations. We recently identified second somatic DICER1 ribonuclease (RNase) IIIb mutations in two MNGs.', 'The objective of the study was to investigate the occurrence of somatic DICER1 mutations and mutational clonality in MNG.', 'MNGs from 15 patients (10 with and five without germline DICER1 mutations) were selected based on tissue availability.', 'Core biopsies/scrapings (n = 70) were obtained, sampling areas of follicular hyperplasia, hyperplasia within colloid pools, unremarkable thyroid parenchyma, and areas of thyroid parenchyma, not classified. After capture with a Fluidigm access array, the coding sequence of DICER1 was deep sequenced using DNA from each core/scraping.', 'All germline DICER1-mutated cases were found to harbor at least one RNase III mutation. Specifically, we identified 12 individually distinct DICER1 RNase IIIb hot spot mutations in 32 of the follicular hyperplasia or hyperplasia within colloid pools cores/scrapings. These mutations are predicted to affect the metal-ion binding residues at positions p.Glu1705, p.Asp1709, p.Gly1809, p.Asp1810, and p.Glu1813. Somatic RNase IIIb mutations were identified in the 10 DICER1 germline mutated MNGs as follows: two cases contained one somatic mutation, five cases contained two mutations, and three cases contained three distinct somatic hot spot mutations. No RNase IIIb mutations were identified in the MNGs from individuals without germline DICER1 mutations.'] Does deep Sequencing reveal Spatially Distributed Distinct Hot Spot Mutations in DICER1-Related Multinodular Goiter?