Current Biomarkers for the Detection of Endometriosis
Endometriosis, defined as the presence of endometrial-like tissue outside the uterine cavity, affects approximately 10% of women of reproductive age and is associated with chronic pelvic pain, infertility, and reduced quality of life. Despite its prevalence, the disease remains challenging to diagnose, often leading to delays of 7–10 years from symptom onset to confirmation. The gold standard for diagnosis remains invasive laparoscopic surgery, underscoring the urgent need for reliable non-invasive biomarkers. Current research focuses on identifying blood, urine, and tissue-based biomarkers, as well as leveraging emerging technologies such as omics platforms and molecular imaging.
Classical Blood Biomarkers
Blood-based biomarkers have been extensively investigated due to their accessibility and clinical feasibility. Among these, cancer antigen-125 (CA-125) is the most studied. Elevated CA-125 levels correlate with advanced-stage endometriosis, with a sensitivity of 1.00 and specificity of 0.80 at a cutoff of >43.0 IU/mL in one study. However, its utility is limited to moderate-to-severe cases, and fluctuations during the menstrual cycle reduce its reliability. Meta-analyses suggest that lower thresholds (e.g., >16.0–17.6 IU/mL) may serve as a SpIN (specificity ≥0.95) triage test but fail to meet criteria for a standalone diagnostic tool.
Cancer antigen-199 (CA-199), another glycoprotein, shows elevated levels in endometriosis but lacks consistency across studies. At a cutoff of >37.0 IU/mL, CA-199 demonstrates a sensitivity of 0.36 and specificity of 0.87, insufficient for clinical use. Similarly, interleukin-6 (IL-6), a pro-inflammatory cytokine, has shown variable results. While one study reported a sensitivity of 0.70 and specificity of 1.00 when combined with tumor necrosis factor-alpha (TNF-α), other studies found no significant association, highlighting the need for multi-analyte approaches.
Urocortin (UCN), involved in endometrial decidualization, has shown promise with specificity reaching 90% at a cutoff of >33 pg/mL. However, heterogeneity among studies precludes definitive conclusions.
A novel approach involves detecting circulating endometrial cells (CECs) in peripheral blood. Using size-based microfluidic chips and immunofluorescence, CECs were identified with 89.5% sensitivity and 87.5% specificity in differentiating endometriosis from benign ovarian masses. Challenges include quantifying CECs and distinguishing them from vascular endothelial or malignant cells. Ongoing single-cell sequencing studies aim to refine CEC specificity.
Emerging Molecular Signatures
Omics technologies (genomics, proteomics, metabolomics) offer high-throughput discovery of novel biomarkers. Proteomic analyses of serum identified six protein peaks (1629.00, 3047.00, 3526.00, 3774.00, 5046.00, and 5068.00 Da) with a sensitivity of 0.66 and specificity of 0.99, meeting SpIN criteria. However, technical complexity and cost limit widespread adoption. Advances in mass spectrometry may improve feasibility.
Metabolomic profiling reveals dysregulation in pathways related to inflammation and oxidative stress. Elevated plasma acylcarnitines, phosphatidylcholines, and sphingomyelins distinguish endometriosis patients, with a diagnostic panel showing 89% accuracy. Follicular fluid alterations, including increased lactate and valine, further highlight metabolic perturbations.
MicroRNAs (miRNAs), small non-coding RNAs regulating gene expression, are dysregulated in endometriosis. Over 40 miRNAs have been studied, with miR-20a, miR-21, and miR-154-5p showing diagnostic potential. A panel including miR-154-5p achieved 92% sensitivity and 76% specificity, though validation in larger cohorts is needed.
Combined Biomarker Panels
Given the complexity of endometriosis, multi-analyte panels outperform single biomarkers. A combination of IL-6 (>15.4 pg/mL) and endometrial PGP 9.5 met criteria for a replacement test (sensitivity ≥0.94, specificity ≥0.79). Similarly, vaginal examination paired with transvaginal ultrasound achieved high specificity for rectovaginal endometriosis. Urinary vitamin D binding protein (VDBP) combined with CA-125 (>2755 IU/mL) also showed promise as a SpIN test.
Urine and Endometrial Biomarkers
Urine-based biomarkers offer non-invasive advantages. Non-neuronal enolase (NNE) and VDBP differentiate endometriosis patients with moderate accuracy, while urinary peptide profiling identified 13 peptides with 82% sensitivity and 76% specificity. However, none meet replacement test criteria.
Endometrial biomarkers, such as PGP 9.5 (a neuronal marker) and aromatase (CYP19), reflect eutopic endometrial dysfunction. PGP 9.5 demonstrated 93% sensitivity and 100% specificity but requires standardized biopsy protocols.
Future Directions
The integration of multi-omics data (genomics, proteomics, metabolomics) and advanced bioinformatics holds promise for identifying biomarker panels. Genome-wide association studies (GWAS) have identified six loci linked to endometriosis risk, though clinical applicability remains distant. Liquid biopsy technologies, including CECs and exosomal miRNAs, may enable real-time monitoring.
Molecular imaging techniques, such as nanoparticle-based targeting of endometriotic lesions, are under exploration. Additionally, machine learning algorithms analyzing multi-modal data (imaging, biomarkers, clinical history) could enhance diagnostic accuracy.
Conclusion
Despite decades of research, no single biomarker meets the stringent criteria for non-invasive endometriosis diagnosis. Current strategies emphasize multi-analyte panels and emerging technologies, with CA-125, CECs, and miRNA profiles leading the field. Urine and endometrial biomarkers offer complementary value, while omics platforms and AI-driven analyses represent future frontiers. Collaborative efforts to standardize methodologies and validate findings in diverse populations are critical to translating research into clinical practice.
doi.org/10.1097/CM9.0000000000001063
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