Diagnostic Value of Pax2 and PTEN Expression in Atypical Endometrial Hyperplasia in the Bulgarian Population

Background: Differentiating atypical endometrial hyperplasia, also known as endometrial intraepithelial neoplasia (EAH/EIN) from endometrial hyperplasia without atypia is crucial due to the higher risk of progression to endometrioid adenocarcinoma, associated with atypical lesions. Immunohistochemical markers such as PAX2 and PTEN have emerged as potential adjuncts to improve diagnostic accuracy in morphologically challenging cases. Objective: To evaluate the diagnostic value of PAX2 and PTEN expression in distinguishing atypical from endometrial hyperplasia without atypia in the Bulgarian population. Materials and Methods: A total of 96 endometrial hyperplasia cases (48 typical, 48 atypical) were included. Histopathological evaluation was performed on hematoxylin and eosin–stained sections, with two experienced pathologists confirming diagnoses according to the WHO criteria. Immunohistochemical analysis of PTEN and PAX2 was conducted on formalin-fixed, paraffin-embedded tissue sections. Results: PTEN expression loss was observed in 6% (3/48) of hyperplasia without atypia cases, compared with 81.3% (38/48) of EAH/EIN cases. For PAX2, strong nuclear staining was retained in 60% (29/48) of endometrial hyperplasia without atypia cases, with no complete loss of expression. In contrast, 64.6% (31/48) of EAH/EIN cases showed complete loss of PAX2 expression, while only 35.4% (17/48) preserved nuclear immunoreactivity. Together, these results highlight clear and consistent differences in PTEN and PAX2 expression between hyperplasia without atypia and EAH/EIN and may aid pathologists in distinguishing these two entities in routine diagnostic practice. Conclusions: Expression loss of PAX2 and PTEN is significantly associated with EAH/EIN. Immunohistochemical evaluation of these markers provides valuable adjunctive information for the diagnosis of morphologically ambiguous cases and may enhance diagnostic reproducibility and accuracy. Incorporating PAX2 and PTEN into routine assessment may guide appropriate clinical management and risk stratification of patients with endometrial hyperplasia.