Michal Zygarowicz,1,* Joanna Kacperczyk-Bartnik,2,3,* Janusz Sierdzinski,4 Cezary Wojtyla,5,6 Piotr Pierzynski,5,6 Grzegorz Manka,7 Mariusz Kiecka,7 Robert Z Spaczynski,8 Piotr Piekarski,9 Beata Banaszewska,10 Artur Jakimiuk,11,12 Tadeusz Issat,13 Wojciech Rokita14,15 ,† Jakub Mlodawski,14,15 Maria Szubert,3,16,17 Piotr Sieroszewski,16,18 Grzegorz Raba,19,20 Kamil Szczupak,19,20 Tomasz Kluz,21 Marek Kluza,21 Michal Lipa,3,22 Damian Warzecha,5,22 Miroslaw Wielgos,23,24 Ewa Koc-Zorawska,25,26 Marcin Zorawski,26,27 Piotr Laudanski5,6,28 1Students’ Scientific Group Affiliated to the Department of Obstetrics, Gynecology and Gynecological Oncology, Medical University of Warsaw, Warsaw, Poland; 2II Department of Obstetrics and Gynaecology, Medical University of Warsaw, Warsaw, Poland; 3Club 35. Polish Society of Gynecologists and Obstetricians, Wrocław, Poland; 4Department of Medical Informatics and Telemedicine, Medical University of Warsaw, Warsaw, Poland; 5OVIklinika Infertility Center, Warsaw, Poland; 6Women’s Health Research Institute, Calisia University, Kalisz, Poland; 7Angelius Provita Hospital, Katowice, Poland; 8Center for Gynecology, Obstetrics and Infertility Treatment Pastelova, Poznan, Poland; 9Division of Infertility and Reproductive Endocrinology, Department of Gynecology, Obstetrics and Gynecological Oncology, Poznan University of Medical Sciences, Poznan, Poland; 10Chair and Department of Laboratory Diagnostics, Poznan University of Medical Sciences, Poznan, Poland; 11Department of Obstetrics and Gynecology, Central Clinical Hospital of the Ministry of Interior, Warsaw, Poland; 12Center of Reproductive Health, Institute of Mother and Child in Warsaw, Warsaw, Poland; 13Department of Obstetrics and Gynecology, Institute of Mother and Child in Warsaw, Warsaw, Poland; 14Collegium Medicum Jan Kochanowski University in Kielce, Kielce, Poland; 15Clinic of Obstetrics and Gynecology, Provincial Combined Hospital in Kielce, Kielce, Poland; 16Department of Gynecology and Obstetrics Medical University of Lodz, Lodz, Poland; 17Department of Surgical Gynecology and Oncology, Medical University of Lodz, Lodz, Poland; 18Department of Fetal Medicine and Gynecology, Medical University of Lodz, Lodz, Poland; 19Clinic of Obstetrics and Gynecology, Provincial Hospital, Przemysl, Poland; 20Department of Obstetrics and Gynecology, University of Rzeszow, Rzeszow, Poland; 21Department of Gynecology, Gynecology Oncology and Obstetrics, Institute of Medical Sciences, Medical College of Rzeszow University, Rzeszow, Poland; 22Department of Obstetrics and Gynaecology, Warsaw Southern Hospital, Warsaw, Poland; 23Premium Medical, Warsaw, Poland; 24Faculty of Medicine, Lazarski University, Warsaw, Poland; 25II Department of Nephrology, Hypertension and Internal Medicine with Dialysis Unit, Medical University of Bialystok, Bialystok, Poland; 26The Academy of Applied Medical and Social Sciences, Elbląg, Poland; 27Department of Cardiology, Lipidology and Internal Medicine with Cardiac Intensive Care Unit, Medical University of Bialystok, Bialystok, Poland; 28Department of Obstetrics, Gynecology and Gynecological Oncology, Medical University of Warsaw, Warsaw, Poland*These authors contributed equally to this work†Professor Wojciech Rokita passed away on March 18, 2020Correspondence: Piotr Laudanski, Department of Obstetrics, Gynecology and Gynecological Oncology, Medical University of Warsaw, Kondratowicza Street 8, Warsaw, 03-242, Poland, Tel +48 22 326 53 80, Email piotr.laudanski@wum.edu.plIntroduction: Endometriosis is an inflammatory-related reproductive age disease characterized by the presence of endometrial cells outside the uterine cavity. Current laboratory practice does not provide specific markers for detecting and assessing the advancement of endometriosis in either plasma or peritoneal fluid. The severity of disease is assessed in stages from I to IV based on the results of laparoscopic inspection. The protein annexin A2 (ANXA2) has been reported to be associated with inflammatory processes.Aim of the Study: The study aimed to investigate and compare ANXA2 protein concentration using the ELISA method in plasma and peritoneal fluid in a group of women with endometriosis compared to controls.Materials and Methods: Biological material was collected during a multicenter, cross-sectional study, which was conducted at eight departments during elective laparoscopy from 53 women with and 40 women without endometriosis. Patients were divided by endometriosis stage and infertility status, and then compared with subgroups. Analysis included the Chi-square test for categorical variables, Mann–Whitney U-test and two-sided Wilcoxon rank-sum test for continuous variables.Results: Women with endometriosis had significantly elevated plasma ANXA2 levels compared to women without endometriosis (mean concentrations 28.69 vs 19.61 ng/L, p=0.01). Differences in peritoneal fluid ANXA2 levels were statistically insignificant (mean concentrations of 23.7 vs 22.97 ng/L, p=0.06). Plasma concentrations in patients with stage III and IV endometriosis were significantly higher compared to controls (mean concentrations of 24.19 vs 19.71 ng/L, p=0.03). No such differences were observed in plasma when comparing stages I–II vs III–IV, and stages I–II vs controls (mean concentrations of 33.82 vs 24.19 ng/L, p=0.72 and 33.82 vs 19.71 ng/L, p=0.12, respectively). Comparison of samples from patients with or without infertility, primary or secondary infertility, endometriosis with or without infertility, and non-endometriosis with or without infertility showed no significant differences in the plasma nor in the peritoneal fluid concentrations.Conclusion: ANXA2 is possibly involved in the pathogenesis of endometriosis, especially in advanced stages. Due to the limited group of tested samples, further studies are needed to confirm its role.Keywords: annexin A2, endometriosis, infertility