Background: Well-differentiated thyroid cancer (WDTC) incidence in pediatrics is rising, most being papillary thyroid carcinoma (PTC). The objective of the study was to assess the prevalence of different mutations in pediatric WDTC and correlate the genotype with the clinical phenotype.Methods: This is a single-center retrospective study. Thyroid tissue blocks from 42 consecutive pediatric WDTC patients who underwent thyroidectomy between 2001 and 2013 were analyzed at Quest Diagnostics for BRAFV600E, RAS mutations (N,K,H), and RET/PTC and PAX8/PPARγ rearrangements, using validated molecular methods. Thyroid carcinomas included PTC, follicular thyroid carcinoma (FTC), and follicular variant of PTC (FVPTC).Results: Thirty-nine samples (29 females) were genotyped. The mean age at diagnosis was 14.7 years (range 7.9–18.4 years), and most were Hispanic (56.4%) or Caucasian (35.9%). The mean follow-up period was 2.9 years. Mutations were noted in 21/39 (53.8%), with both BRAFV600E (n = 9), and RET/PTC (n = 6) detected only in PTC. Mutations were detected in 2/5 FTC (PAX8/PPARγ and NRAS) and 3/6 FVPTC cases (PAX8/PPARγ). Of 28 PTC patients, 57.1% had mutations: 32.1% with BRAFV600E, 21.4% with RET/PTC, and 3.6% with NRAS. Of patients with BRAFV600E, 77.8% were Hispanic and 88.9% were >15 years, while all RET/PTC-positive patients were ≤15 years (p = 0.003). Tumor size, lymph node involvement, and distant metastasis at diagnosis (or soon after 131I ablation) did not vary significantly based on the mutation.Conclusions: BRAFV600E was the most common mutation, especially in older and Hispanic adolescents. A larger, ethnically diverse pediatric cohort followed long term will enable the genotypic variability, clinical presentation, and response to therapy to be better assessed.

In the barn owl, maps of interaural time difference (ITD) are created in the nucleus laminaris (NL) by interdigitating axons that act as delay lines. Adult delay line axons are myelinated, and this myelination is timely, coinciding with the attainment of adult head size, and stable ITD cues. The proximal portions of the axons become myelinated in late embryonic life, but the delay line portions of the axon in NL remain unmyelinated until the first postnatal week. Myelination of the delay lines peaks at the third week posthatch, and myelinating oligodendrocyte density approaches adult levels by one month, when the head reaches its adult width. Migration of oligodendrocyte progenitors into NL and the subsequent onset of myelination may be restricted by a glial barrier in late embryonic stages and the first posthatch week, since the loss of tenascin-C immunoreactivity in NL is correlated with oligodendrocyte progenitor migration into NL.

5510 Background: In 2009, the American Thyroid Association revised its guidelines for patients with thyroid nodules and differentiated thyroid cancers, recommending BRAF, RAS, RET/PTC, and PAX8-PPARγ molecular testing in patients with indeterminate fine-needle aspirate (FNA) cytology. Alterations in any of these markers in thyroid nodules are strongly associated with malignancy. We studied the prevalence of these alterations in thyroid FNA specimens in order to establish a strategy to improve disease management. Methods: DNA and RNA were extracted from thyroid FNA specimens (N=149) and tested for BRAF mutations using allele-specific PCR (V600E and K601E); for RAS (H-, K-, N-) mutations using pyrosequencing (codons 12, 13, and 61); and for RET/PTC1 and RET/PTC3 rearrangements and PAX8-PPARγ translocations using RT-PCR. Results: Overall, 90 (60.4%) of the specimens had alterations in ≥1 of the 4 molecular markers (Table). BRAF V600E mutations (54.4%) were the most prevalent mutations in papillary thyroid cancer (PTC); no K601E mutations were found. RAS mutations were found in PTC, follicular adenoma (FA), and follicular thyroid cancer (FTC) specimens; half of these mutations involved N-RAS Q61. RET/PTC rearrangements were detected in 3.5% of PTC specimens and were evenly distributed between the 2 major subtypes, RET/PTC1 and RET/PTC3. PAX8/PPARγ translocations were detected in 18.8% of FTC but not in FA, probably due to small sample size. Out of 7 indeterminate thyroid nodules, 2 had BRAF mutations and 2 had RAS mutations. The presence of the 4 markers was generally mutually exclusive; only 1 PTC specimen had concurrent RAS and RET/PTC1 alterations. Conclusions: The prevalence of BRAF, RAS, RET/PTC, and PAX8/PPARγ alterations in thyroid cancer specimens highlights the potential for targeted therapeutic strategies. The mutually exclusive pattern of alterations also suggests a hierarchical screening strategy for samples with limited availability. [Table: see text]

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