Immunohistochemical assessment of YAP1 expression in endometrial hyperplasia with and without Atypia

Abstract

Aim: Endometrial hyperplasia, particularly when accompanied by atypia, is considered a well-established precursor of endometrial carcinoma. Yes-associated protein 1 (YAP1), a key effector of the Hippo signaling pathway, plays a crucial role in the regulation of cell proliferation, apoptosis, and tissue homeostasis and has been implicated in tumorigenesis. The present study aimed to investigate whether YAP1 protein expression in endometrial hyperplasia with and without atypia differs from that in normal endometrial tissue. Methods: This retrospective observational case-control study included 122 patients: 41 cases of endometrial hyperplasia with atypia, 41 cases of endometrial hyperplasia without atypia, and 40 controls with normal endometrial histology. Immunohistochemical analysis was performed on formalin-fixed, paraffin-embedded tissue sections using a YAP1 polyclonal antibody. Staining localization (nuclear and/or cytoplasmic), intensity, and distribution were evaluated semi-quantitatively. Statistical comparisons among the three groups were performed using parametric or nonparametric tests according to the distribution characteristics of the variables. Results: No statistically significant differences were observed among the study groups in terms of YAP1 staining localization, intensity, or distribution. Both nuclear and cytoplasmic expression patterns were comparable in endometrial hyperplasia with and without atypia and in control tissues. Conclusion: Yes-associated protein 1 protein expression did not differ significantly between precancerous endometrial lesions and normal endometrium. These findings suggest that YAP1 activation may represent a later molecular event in endometrial carcinogenesis rather than an early alteration during precursor stages. Further prospective studies integrating molecular and functional analyses are warranted to clarify the precise role of YAP1 in the progression from benign to malignant endometrial pathology.