Outcome of Subclassification of Indeterminate (Thy-3) Thyroid Cytology into Thy-3a and Thy-3f

Abstract

Objectives: The British Thy system is a widely used classification system for reporting thyroid fine-needle aspiration (FNA) cytology. The Royal College of Pathologists in 2009 recommended the subdivision of the Thy-3 (indeterminate) category into Thy-3a (atypia) and Thy-3f (follicular neoplasm). Our objective was to examine the malignancy rates of Thy-3a and Thy-3f cases at our institution and to investigate whether the risk of malignancy in Thy-3a cases is reduced by FNA on a different occasion showing benign cytology. Methods: This is a retrospective study of 748 thyroid nodules undergoing 1,032 FNAs, with indeterminate (Thy-3) cytology subdivided into Thy-3a and Thy-3f. Cases were correlated with final histology in surgical cases. Incidental carcinomas occurring outside the biopsied nodule were discounted. Results: A total of 109 nodules had a final cytological diagnosis of Thy-3a, of which 67 underwent surgery, with an incidence of malignancy of 13.4% (9/67); 90 nodules had a final cytological diagnosis of Thy-3f, of which 84 underwent surgery, with an incidence of malignancy of 17.9% (15/84). The difference in malignancy rates was not significant (p = 0.51). The incidence of malignancy in nodules with benign and Thy-3a cytology on separate occasions was not significantly different from cases with a single Thy-3a cytology. Conclusions: Thyroid nodules with Thy-3a cytology have a slightly lower risk of malignancy than Thy-3f cases. However, the difference is not significant and does not appear to be reduced by FNA on a separate occasion showing benign cytology. Management decisions for patients with Thy-3a cytology should be taken carefully to avoid missing cancers.

When Is Thyroidectomy the Right Choice? Comparison between Fine-Needle Aspiration and Final Histology in a Single Institution Experience

“…A further analysis showed that among TIR3A and TIR3B there is no significant difference between patients with and those without cancer in terms of age (TIR-3A: 58.78 vs. 53.31 years, p = 0.31; TIR-3B: 50.68 vs. 52.33 years, p = 0.65), as already shown by Brophy et al [16] .…”

“…• The TIR-3B (high-risk indeterminate lesion) subcategory included: -specimens with high cellularity in a monotonous and repetitive microfollicular/trabecular arrangement, with scant or absent colloid; -samples composed exclusively or almost exclusively of Hürthle cells [10] ; -samples characterized by nuclear alterations suggestive of papillary carcinoma, but too mild or focal to be included in the TIR-4 category [16] . The TIR-3B subcategory should have a frequency lower than 10% and its cancer risk between 20 and 30% [9] .…”

Atypia of Undetermined Significance in Thyroid Fine Needle Aspirates: a 4-Year Audit of Thy3a Reporting

“…Our 7% malignancy rate is also below their 17% standard. At another similar institution, their Thy3a study [6] reported a higher incidence of Thy3a usage. This retrospective study of 748 thyroid nodules saw 109 being reported as Thy3a with a malignancy rate of 13.4%.…”

Extending expressed RNA genomics from surgical decision making for cytologically indeterminate thyroid nodules to targeting therapies for metastatic thyroid cancer

“…Consequently, even with ultrasound and cytological examination, the character of thyroid nodules remains uncertain in approximately 1 in 7 thyroid patients. When a cytologically indeterminate nodule has been identified by an expert cytopathologist, doubt exists that the risk of cancer can be sufficiently reduced to avoid surgery through repeat biopsy, review by a second cytopathologist, further subclassification of the indeterminate category, or correlation with thyroid nodule ultrasound classification …”