Epithelial–mesenchymal phenotypic heterogeneity in endometriotic lesions

• EMT-related markers show marked heterogeneity across endometriotic lesions • Distinct epithelial, mesenchymal-enriched, and mixed phenotypic patterns were identified • E-cadherin, N-cadherin, and vimentin display variable expression at the lesion level • No correlation was observed between gene expression and protein markers • Findings support EMT-related phenotypic variability rather than a uniform transition Epithelial-mesenchymal transition (EMT) markers have been reported as altered in endometriosis compared to eutopic endometrium; however, findings remain inconsistent, possibly due to the the marked heterogeneity of endometriotic lesions. This study aimed to characterize the expression patterns of EMT-related markers in a series of well-characterized endometriotic lesions. The study enrolled 14 women with ages between 20 and 45 years scheduled for laparoscopy to treat endometriosis, and lesions came from biopsies of the following pelvic structures: rectum/sigmoid (n = 8), uterosacral ligament (n = 1), ureter (n = 1), and peritoneum (n = 4). In addition, eight endometrial biopsies from women with (n = 4) and without (n = 4) endometriosis were used as positive controls for the immunostaining of EMT markers. The expression of E-cadherin, N-cadherin, and vimentin was evaluated by immunohistochemistry, and gene expression of CDH1, CDH2, SNAI1, and ZEB1 was assessed by quantitative PCR E-cadherin, N-cadherin, and vimentin were detected in 50%, 60%, and 70% of endometriotic lesions, respectively, with marked variability in intensity and spatial distribution. Distinct molecular phenotypes were identified, including epithelial-dominant, mesenchymal-enriched, and mixed epithelial–mesenchymal patterns. These findings reflect the co-occurrence of epithelial and mesenchymal features at the lesion level rather than confirmed co-expression within individual cells. No significant correlation was observed between gene expression and protein levels. Endometriotic lesions exhibit marked epithelial–mesenchymal phenotypic heterogeneity. These findings support the concept of EMT-related variability at the lesion level rather than a uniform or fully established transition, highlighting the complexity of EMT-related processes in endometriosis.