Evaluation of EZH1 Expression in Thyroid Tumors with a Follicular Pattern: An Immunohistochemical and Morphometric Study

Background Differentiating follicular-patterned thyroid tumors remains challenging in routine pathology. Enhancer of Zeste Homolog 1 (EZH1) plays a role in thyroid tumorigenesis, and its mutations are reported predominantly in benign follicular-patterned tumors. This study aimed to evaluate EZH1 expression across different histopathological subtypes of thyroid tumors and to investigate its relationship with morphometric parameters. Methods A total of 125 follicular-patterned thyroid tumors diagnosed between 2011 and 2021 were retrospectively analyzed. Clinical and histopathological data were collected. EZH1 immunohistochemistry was performed and scored using the H-score method. Morphometric measurements (capsular thickness, follicle diameter, and follicle count) were obtained. Data were statistically evaluated with Chi-square, ANOVA, and correlation analyses. Results Of the patients, 76% were female, with a mean age of 48.5 years. The thickest capsule was observed in OCs (0.88 mm), while the largest follicle diameter was detected in FAs (92.6 µm). EZH1 H-scores did not significantly differ among histological subtypes overall. However, strong (3+) EZH1 expression predominated in FAs and OAs, whereas moderate (2+) staining was more frequent in PTC subtypes. This staining pattern was statistically significant for differentiating benign from malignant follicular-patterned tumors. Conclusion EZH1 mutations are more common in benign thyroid tumors. To our knowledge, our study is the first to investigate EZH1 expression levels in different histological subtypes of thyroid tumors. In order to understand the genotype-phenotype relationship in thyroid tumors, new studies are needed to investigate the EZH1 mutation-expression relationship as well as morphometric studies.