Interpretation of low-risk neoplasms in the 5th edition of WHO classification of thyroid tumors

Abstract

The fifth edition of World Health Organization (WHO) classification of thyroid tumors replaced the "borderline tumors" in the fourth edition with "low-risk tumors", including noninvasive follicular thyroid neoplasms with papillary-like nuclear features, uncertain malignant potential and hyalinizing trabecular tumors. All of them are thyroid tumors with follicular epithelial cell origin, capsule/clear boundary, no lymph node and distant metastasis (EX0, N0, M0). The spread probability of "low-risk tumor" is extremely low, and this new classification can protect the pathologists from medical litigation when encountering rare and special metastatic cases. Based on the interpretation of the thyroid tumor classification, this paper further discussed several low-risk tumors, which were not listed in the current WHO classification.