Objectives: Endometrioid and clear cell ovarian adenocarcinomas are suspected to derive from ectopic endometrial foci. The aim of the study was to determine PTEN and MMP-2 immunoexpression in endometrial ovarian cysts, endometrioid and clear cell ovarian carcinomas and to assess the relationship between the abovementioned values and clinical data of patients in order to find the marker of increased risk of malignant proliferation based on ovarian endometriotic lesions. Detailed analysis of the collected data was conducted to investigate the correlation between immunohistochemical expression of the examined antigens, histopathological diagnosis and clinical condition of patients. Material and methods: 20 endometrial adenocarcinomas, 21 clear cell ovarian cancers and 26 endometrial cysts were included in the study. The control group consisted of 29 specimens of physiological endometrium: 16 samples of the proliferative phase and 13 samples of the secretory phase. Protein expression of PTEN and MMP-2 was evaluated by immunohistochemistry. Protein immunoexpression in the collected specimens was estimated with the use of light microscope and MultiScan software. Immunoreactivity of the PTEN antigen was assessed by the quantitative method, whereas MMP-2 immunoexpression was evaluated by the semi-quantitative method. Two-sided tests were used for statistical inference. Generalized linear models were used to compare the studied groups. Error distributions were selected using the Akaike criterion (AIC). Statistical analysis was conducted with the use of the R Statistical Package. Results: MMP-2 immunoreactivity differed significantly between the study groups and controls (p<0.001). PTEN immunoexpression was the strongest in endometrial cysts (53.7 %), lower in clear cell cancers (50.2%) and the lowest in endometrioid adenocarcinomas (43.88%), but the differences were not statistically significant (p=0.17). PTEN reactivity in the group of endometrioid carcinomas was significantly higher (p=0.02), while MMP-2 expression had a falling tendency (p=0.076) in obese women. Conclusions: Increased MMP-2 expression in the successive groups may imply a rising invasive potential of the epithelial cells in endometrial cysts, endometrioid and clear cell adenocarcinomas. Strong immunoreactivity for PTEN in proliferative endometrium implies its role in the regulation of endometrial proliferation. PTEN activity may reduce MMP-2 expression in insulin resistant women suffering from endometrial ovarian cancer. Simultaneous evaluation of PTEN and MMP-2 immunoexpression in ectopic endometrial foci cannot be used to identify women with an increased risk of neoplastic transformation.