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Background and aimsAppendiceal neoplasms are uncommon entities that are usually determined incidentally during the histopathological examination. Different techniques used for the macroscopic sampling of appendectomy material may affect the determinating neoplasms.Materials and methodsH&E-stained slides of 1280 cases who underwent appendectomy between 2013 and 2018 were reviewed retrospectively for histopathological features.ResultsNeoplasms were determined in 28 cases (3.09%); 1 lesion was observed in the proximal part of the appendix, 1 covering the entire length from proximal to distal and 26 in the distal part. In the 26 cases that observed in the distal part, the lesion was seen on both sides of the longitudinal section of the distal appendix in 20 cases, while it was seen on only one distal longitudinal section in the remaining 6 cases.ConclusionThe vast majority of appendiceal neoplasms are seen in the distal part of the appendix, and, in some cases, neoplasms might be seen on only one side of the distal section. Sampling only one-half of the distal part of the appendix, where tumours are most often observed, could result in some neoplasms being missed. Therefore, sampling the whole distal part would be more beneficial to determine small diameter tumours that do not create macroscopic findings.

Some pediatric papillary thyroid carcinoma (PPTC) cohorts have suggested a preliminary correlation with respect to DICER1 mutation status and histomorphology in both benign and malignant follicular cell-derived nodules; however, the data regarding correlates of DICER1-related sporadic PPTCs subtyped based on the 2022 WHO classification criteria are largely unavailable. The current study investigated the status of hotspot DICER1 mutations with clinical, histological and outcome features in a series of 56 patients with PPTCs with no clinical or family history of DICER1-related syndromic manifestation. Fifteen (27%) PPTCs harbored BRAF p.V600E. Eight (14%) cases of PPTCs harbored DICER1 mutations with no associated BRAF p.V600E. DICER1 mutations were identified in exons 26 and 27. A novel D1810del (c.5428_5430delGAT) mutation was also detected. We also confirmed the absence of hotspot DICER1 mutations in the matched non-tumor tissue DNA in all 8 DICER1-related PPTCs. The mean age of DICER1-harboring PPTCs was 15.1 (range: 9-18) years whereas the rest of this cohort had a mean age of 14.8 (range 6-18) years. With the exception of one PPTC, all DICER1-related PPTCs were seen in females (female-to-male ratio: 7). The female to male ratio was 3.8 in 48 DICER1-wild type PPTCs. In terms of histological correlates, 5 of 8 (63%) DICER1-mutant PPTCs were invasive encapsulated follicular variant papillary thyroid carcinomas (FVPTCs) including 4 minimally invasive FVPTCs and 1 encapsulated angioinvasive FVPTC, whereas the remaining 3 PPTCs were infiltrative classic papillary thyroid carcinomas (p < 0.05). The incidence of DICER1 mutations was 19.5% in BRAF p.V600E-wild type PPTCs. Sixty-three percent of DICER1 hotspot mutations occurred in invasive encapsulated FVPTCs, and this figure represents 38% of invasive encapsulated FVPTCs. Only one (12%) patient with DICER1-related disease showed a single lymph node with micro-metastasis. Unlike DICER1-wild type patients, no distant metastasis is identified in patients with DICER1-related PPTCs. The current series expands on the surgical epidemiology of somatic DICER1related PPTCs by correlating the mutation status with the clinicopathological variables. Our findings underscore that female gender predilection and enrichment in low-risk follicular-patterned PTCs are characteristics of DICER1-related PPTCs. KeywordsDICER1 • Follicular adenoma • Follicular nodular disease • Multinodular hyperplasia • Differentiated thyroid carcinoma • Papillary thyroid carcinoma • Pediatric thyroid carcinoma • Pediatric papillary thyroid carcinoma • BRAF p.V600E * Semen Onder

• Synovial sarcoma (SS) occurs primarily in the para-articular regions of the extremities and accounts for 5-10% of all human sarcomas. Primary involvement of the thyroid (primary SS of the thyroid), however, is very rare. • Almost all SSs reveal a specific chromosomal change [t(X; 18) (p11.2; q11.2)], which results in the expression of a chimeric SYT-SSX gene transcript. Novel Insights • Despite its bland cytologic features, PSST is a very aggressive tumor, showing a high proliferative activity with a mitotic index up to 40/10 high-power fields. • The main diagnostic pitfall of PSST is SETTLE. The presence of mitotic figures and basal lamina material in cytologic material, negative immunostaining for smooth muscle actin (SMA), and positive staining for transducer-like enhancer of split 1 (TLE-1) antibody favor SS over SETTLE. • In order to avoid potential traps in these cytologically bland neoplasms, all diagnostic clues, including molecular techniques, should be evaluated, in view of the therapeutic and prognostic implications.

Objective: Although squamous cell carcinomas (SCCs) originating from different anatomic localizations display a similar histological appearance under light microscopy, they may differ in terms of epigenetic and genetic features. The aim of this study was to analyze mir-126, mir-182, and mir-486-5p expression levels in head and neck SCCs and lung SCCs, and to identify localization-specific miRNA expression profiles. Material and Method: The expression levels of mir-126, mir-182, and mir-486-5p were analyzed in lung, oral cavity, laryngeal, and hypopharyngeal SCCs in 40 patients, using quantitative real-time polymerase chain reaction. Results: The findings showed that lung, oral cavity, laryngeal, and hypopharyngeal SCCs have distinct mir-126 and mir-486-5p expression profiles. It was also observed that mir-126 and mir-486-5p expression levels were highly specific to the tumor localization. Conclusion: These findings highlighted that SCCs originating from different anatomic localizations have different miRNA expression profiles. miRNA expression analysis can be used to predict the primary localizations of those SCCs.