Endometriosis is a hormone-dependent gynecological disorder that is defined by the presence of ectopic endometrial tissues [1,2]. Because of difficulties in endometriosis diagnosis, its exact frequency is mainly unknown in the general population but it is estimated around 10–15% of reproductive-age women and 30–50% in infertile women [3]. Although many gaps remain in understanding the precise etiology of this disease, current evidence proposes that endometriosis is a multifactorial disease and the environmental factors may perform important roles [4].

Endocrine-disrupting chemicals (EDCs) are a general group of chemicals that have negative effects on hormones action. Exposure to these chemicals including organochlorine pesticides (OCPs), bisphenol A (BPA), and polychlorinated biphenyls (PCBs) exerts adverse impacts on many aspects of human health, especially fertility [5]. PCBs are a type of environmental toxins that contain more than 200 congeners [6]. PCBs are described to be lipophilic, resistant to environmental destruction, and bio-accumulative within food chains. The production of these chemicals has been banned since the 1970s but, because of their properties, PCBs are still detected in human fatty tissue and blood [7,8]. PCBs may interfere with the endocrine system via the competitive binding to estrogen/androgen receptors and or may act on the aryl hydrocarbon receptor (AhR) pathway and then perform a cross impact on the estrogen receptor pathway [5,7].

Numerous studies have examined the association between EDCs exposure and endometriosis risk [9], [10], [11]. Some studies reported that exposure to PCBs is associated with endometriosis (odds ratio (OR) = 6.5, 95% confidence intervals (CI): 1.5–28 [12] and OR = 4.64; 95% CI: 1.93–11.16 [10]), however; some other studies indicated that there is no association between PCBs exposure and endometriosis risk (OR = 1.2; 95% CI: 0.6–2.3 [13] and OR = 1.08; 95% CI: 0.43-2.73 [14]). The inconsistent results of these studies are often due to methodological limitations and population heterogeneity. Recently, two meta-analyses were carried out on human epidemiological evidence regarding the relationship between EDCs exposure, particularly PCBs, and endometriosis risk; however, their results are inconclusive [3,15]. One of them was a meta-analysis (without comprehensive systematic review) that included 12 studies for PCBs published before 1 January 2018 from PubMed, EMBASE, and Web of Science (OR = 1.58; 95% CI: 1.18-2.12) [3]. Another study was a systematic review and meta-analysis that included 9 studies for PCBs from PubMed and Web of Science until August 2018 (OR = 1.70; 95% CI: 1.20-2.39) [15]. Both studies exerted the English language limitation. The included primary studies in these meta-analyses had different diagnostic methods for confirmation of endometriosis such as laparoscopy, surgery, and self-reported questionnaires and evaluated PCB levels in serum and adipose tissue. The statistical heterogeneity of both studies is more than 50 % [3,15].

In the current study, we performed an electronic search in different databases and we extended the search time interval. To reduce methodological heterogeneity, we included only articles that had investigated PCB levels in serum and the endometriosis diagnostic methods were laparoscopy and surgery based on the pathology report. Therefore, to summarize recent findings and collect more solid evidence for a deeper understanding of the association between human exposure to PCBs and the risk of endometriosis, the present systematic review and meta-analysis was conducted.