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AIMS: While CAP and ICCR protocols mandate the separation of angioinvasion (AI) and lymphatic invasion (LI) in thyroid carcinoma, distinction between them can be difficult. Because the presence of AI is used to stratify patients with papillary thyroid carcinoma (PTC), there is a need to accurately diagnose AI and LI. METHODS AND RESULTS: AI and LI were evaluated in 162 cases of PTC (n = 155) and high-grade differentiated thyroid carcinoma, papillary phenotype (HGDTCp, n = seven) using haematoxylin and eosin (H&E), D2-40 and CD31/ERG. In encapsulated carcinomas, vascular invasion (VI) was only of AI nature. Infiltrative carcinomas showed LI (46 of 131, 35%) and AI (19 of 131, 16%). The frequency of nodal metastasis (NM) and large volume of NM was 93 and 85%, respectively, in tumours with LI, and 39 and 26%, respectively, in those without LI. Luminal red blood cells and smooth muscle in the wall of large-calibre vessels were not reliable criteria to exclude LI and were seen in 23 and 6% of LI, respectively. LI was an independent predictor for NM, whereas AI is an independent predictor for distant metastasis at presentation in PTC/HGDTCp. CONCLUSION: VI in encapsulated carcinomas, including follicular variant PTC, is only of AI nature, confirming the position of this variant as a close entity to follicular carcinoma rather than classic PTC, whereas infiltrative PTC/HGDTCp may have LI or, less frequently, AI. As no morphological features reliably distinguish LI from AI, D2-40 and CD31/ERG immunostains should be considered for separating AI from LI when dealing with vascular invasion in an infiltrative PTC.
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PURPOSE: Seizure-related 6 homolog (SEZ6) is a cDNA that strongly associated with neuroendocrine differentiation. Recently, SEZ6 expression was found in a subset of small cell lung carcinoma (SCLC). Furthermore, ABBV-011, a novel antibody drug conjugate targeting SEZ6 has been developed and is currently in clinical trial in treating SCLC and neuroendocrine neoplasms, including medullary thyroid carcinoma (MTC). We herein presented the first evidence that SEZ6 was highly expressed in MTC. METHODS: SEZ6 immunoexpression was studied in 78 MTCs and correlated with clinicopathologic characteristics, outcome, and molecular profile. RESULTS: SEZ6 was highly expressed in primary tumors, regional recurrence, and distant metastasis. Using two different SEZ6 antibody clones SC17.14 and 14E5, SEZ6 immunopositivity was seen in 91% to 93% of primary MTCs, 100% of regional recurrence, and 75% to 83% of distant metastasis. High level of SEZ6 immunoexpression determined using H score was associated with male sex, advance stage, and extrathyroidal thyroidal extension. There was no correlation between SEZ6 expression and outcome or RET/RAS mutation status in MTC. The frequency of SEZ6 positivity in MTC without RET/RAS mutations were 83%. MAIN CONCLUSIONS: SEZ6 may serve as a novel biomarker for MTCs. Although SEZ6 lacks any prognostic values in MTC, its positivity in 91% to 93% of MTCs, including MTCs without RET and RAS mutations, renders SEZ6-targetted antibody-drug conjugate therapy a promising targeted therapy for MTCs.