Impact of the Reclassification of the Non-Invasive Follicular Variant of Papillary Carcinoma as Benign on the Malignancy Risk of the Bethesda System for Reporting Thyroid Cytopathology: A Meta-Analysis Study

Abstract

Objectives: The Bethesda System for Reporting Thyroid Cytopathology (TBSRTC) established diagnostic categories for cytologic specimens of the thyroid. Each category was associated with an estimated risk of malignancy. Recently, the non-invasive follicular variant of papillary thyroid carcinoma has been reclassified as benign. This reclassification may alter the malignancy risk of TBSRTC diagnostic categories. Study Design: A literature search was made for all studies investigating the effect of reclassification of some non-invasive follicular variant papillary thyroid carcinomas as benign on the malignancy risk associated with TBSRTC categories. The authors calculated the malignancy risk for TBSRTC categories in a series of 315 thyroid aspirates when the non-invasive follicular variant of papillary thyroid carcinoma was considered benign. A meta-analysis of malignancy risk data for the 3 published studies and the current study was performed. Results: The meta-analysis showed that the malignancy risk was reduced for all TBSRTC categories except the “non-diagnostic” category. The reduction in malignancy risk was greatest in the categories “suspicious for malignancy” and “atypia/follicular lesion of undetermined significance.” Conclusion: A meta-analysis of all pertinent studies demonstrated that re-categorization of the non-invasive follicular variant of papillary thyroid carcinoma as benign reduces the malignancy risk in the majority of TBSRTC categories.