Background <p>Endometriosis is a systemic, estrogen-dependent inflammatory disorder affecting approximately 10% of women of reproductive age and is even more common among those with chronic abdominal pain and infertility. Despite research advances, understanding its pathogenesis and distinguishing endometriotic cysts remain challenging. Prostate-specific membrane antigen (PSMA), traditionally used in the imaging and treatment of prostate cancer, has been detected in various benign and malignant conditions. This study evaluated PSMA expression in endometriosis tissues as a marker to differentiate ovarian endometriotic cysts from other cysts.</p> Methods <p>Formalin-fixed, paraffin-embedded tissue samples from 10 patients with histopathologically confirmed endometriosis who underwent surgery in 2023 were analyzed. Tissue sections were stained with hematoxylin and eosin, and immunohistochemical analysis was performed using an antibody against PSMA. PSMA expression was assessed in microvascular endothelial cells and non-endothelial cells using a semi-quantitative immunoreactivity scoring system. In addition, a case study involving Gallium-68-labeled PSMA positron emission tomography/computed tomography (PET/CT) imaging was conducted in one patient.</p> Results <p>PSMA immunostaining was positive in 28 of 33 endometriosis tissue samples. Notably, strong and diffuse PSMA expression was observed exclusively in the microvessels of ovarian endometriotic cyst capsules, with all 11 slides of this subtype demonstrating high vascular expression. In contrast, no PSMA expression was detected in other ovarian cyst types, such as follicular and corpus luteum cysts. Weak PSMA staining in non-endothelial cells was noted in 15 slides, primarily within endometrial glands in cases of scar endometriosis and in fallopian tubes. High vascular PSMA expression was unique to ovarian endometriosis among the three forms evaluated (scar, tubal, and ovarian). Two out of five uterine fibroid samples also exhibited high vascular PSMA expression, while the rest showed low expression. The PET/CT examination confirmed significant tracer accumulation in an ovarian endometriotic cyst.</p> Conclusions <p>The study demonstrates that PSMA expression is predominantly localized to the microvessels of ovarian endometriotic cyst capsules, effectively distinguishing them from other ovarian cysts. The limited or absent PSMA staining in non-ovarian endometriosis supports its potential role as a diagnostic marker. These findings warrant further investigation into the utility of PSMA in imaging and possibly therapeutic targeting of ovarian endometriosis.</p>