Defining angioinvasion and lymphatic invasion in papillary thyroid carcinoma: morphological criteria, utility of D2-40/CD31/ERG immunohistochemistry and correlation with clinicopathological characteristics.

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.