Different Threshold of Malignancy for -like Thyroid Tumors Causes Significant Differences in Thyroid Nodule Practice.

Histopathological diagnosis of papillary thyroid carcinomas (PTCs) is prone to significant observer variation due to different thresholds of -like nuclear changes among pathologists. This gap recently widened due to a defensive attitude by Western pathologists where malpractice litigation is significant. Cases with delicate -like nuclear changes are follicular adenomas when they are noninvasive, follicular carcinomas when invasive, and follicular variant PTCs when they have fully developed PTC-type nuclear features in Asian practice. The different diagnostic threshold of PTC nuclear features resulted in a high (50-90%) incidence of mutation of PTCs in most Asian countries, whereas it was low (35-50%) in most Western patient cohorts. The contamination of indolent -like tumors in the malignant PTC category in Western patient cohorts explains why the gene test identifies aggressive PTCs. However, the test has no prognostic value for Asian PTC patients because most biologically benign or low-risk -like tumors are excluded from PTC. All prognostic analyses of thyroid carcinomas before 2017 must be re-evaluated because most clinical guidelines were established based on data obtained from Western patient cohorts where a significant number of indolent -like tumors were misclassified in the malignant category.