Endometriosis is an estrogen-dependent inflammatory disease affecting women in their reproductive age. Due to non-specific symptoms, women with endometriosis are often misdiagnosed or are accurately diagnosed only after several years. Diagnosis of peritoneal endometriosis is especially challenging and relies only on laparoscopic surgery. To date, different molecules have been proposed as potential non-invasive biomarkers of endometriosis; however, none have been confirmed as clinically useful. Therefore, this study aimed to discover novel plasma biomarker candidates for peritoneal endometriosis using an antibody array platform. This study included patients with endometriosis-like symptoms characterized by the absence (controls) or presence of peritoneal endometriosis (cases) after laparoscopic surgery and histological evaluation. Patients were further divided into secretory and proliferative groups, according to the phase of their menstrual cycle. Their plasma samples were collected and analyzed on an antibody array platform targeting more than 1350 proteins with over 1820 antibodies. In the proliferative group, the analysis revealed three differential proteins between cases and controls: ITB3, ITA2B2, and ACVL-1. In the secretory group, none of the examined proteins reached the log-fold change (logFC) and significance thresholds simultaneously. The potential of the identified differential proteins as plasma biomarker candidates for peritoneal endometriosis should be evaluated on a larger cohort, and their role in endometriosis should be investigated in further studies.

Growth arrest-specific protein 6 (GAS6) has an important role in regulating the immune system. Recent studies have revealed its association with the pathophysiology of endometriosis and identified GAS6 as one of the hub genes and a biomarker candidate. Endometriosis is a common chronic inflammatory gynaecological disease of women of childbearing age. Due to surgical diagnosis, non-invasive biomarkers are urgently needed. We investigated GAS6 as a candidate biomarker for the diagnosis of endometriosis. Our case–control study included 284 patients and showed that plasma levels of GAS6 are significantly higher in patients with endometriosis compared to control patients. We calculated logistic regression models using GAS6, CA-125, and GAS6 together with CA-125, and added a series of clinical and lifestyle data collected before surgical diagnosis. A CA-125 model and a model including GAS6 and CA-125 showed the highest AUC values of 0.745 ± 0.04, while the model including CA-125, data on sport/recreation before surgery, and dysmenorrhea score reached an AUC of 0.767 ± 0.04. Our results indicate that GAS6 is increased in patients with endometriosis, but it cannot serve as a biomarker candidate.