4.1 Medicine 

Features of Immunohistochemical Expression of Melatonin MT1 Receptor in Epithelial Ovarian Tumors

Melatonin receptor MT1 ovarian epithelial tumours ovarian carcinoma high-grade serous carcinoma immunohistochemistry ovarian cancer tumour heterogeneity

Authors

June 4, 2026

Melatonin exerts multiple biological effects through its membrane receptors, particularly Melatonin Receptor 1 (MT1), which has been implicated in the regulation of cellular proliferation, apoptosis, oxidative stress, and tumour progression. However, the expression profile of MT1 in ovarian epithelial tumours remains insufficiently characterised.  To investigate the immunohistochemical expression of MT1 in ovarian epithelial tumors and evaluate its distribution across different histological subtypes and stages of tumor progression. A retrospective immunohistochemical study was performed on ovarian epithelial tissue specimens representing normal ovarian surface epithelium, benign serous cystadenoma, serous borderline tumour, low-grade serous carcinoma, high-grade serous carcinoma, and endometrioid carcinoma. MT1 expression was assessed using immunohistochemistry and quantified by H-score methodology based on staining intensity and the percentage of positive tumour cells. MT1 expression was detected in all examined groups but demonstrated substantial heterogeneity among histological subtypes. Normal ovarian epithelium showed low expression, while benign serous cystadenomas and serous borderline tumours demonstrated moderate expression. The highest MT1 expression was observed in high-grade serous carcinoma, whereas endometrioid carcinoma exhibited the lowest expression levels. MT1 expression was therefore not associated with a gradual decrease during malignant transformation but rather displayed a subtype-specific distribution pattern.

MT1 expression in ovarian epithelial tumours is characterised by significant histological heterogeneity. High-grade serous carcinoma demonstrates marked MT1 overexpression compared with other epithelial ovarian tumour subtypes. These findings suggest that MT1 may be associated with subtype-specific biological mechanisms rather than serving as a simple marker of tumour progression.

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