Seminal Fluid Biomarkers for Early Cancer Detection: A Systematic Review

Background: The early detection of prostate and testicular tumors remains challenging as standard diagnostic tools often lack sensitivity and produce ambiguous results. Seminal fluid is a biologically rich medium that closely reflects the state of male reproductive tissues and has therefore emerged as a promising source of non-invasive molecular biomarkers. Objective: This study aimed to critically evaluate the evidence regarding cell-free DNA, RNA, proteins and metabolites in seminal fluid, and to assess their potential for improving the early detection of male reproductive cancers. Methods: A systematic review was performed according to PRISMA guidelines. Comprehensive searches of the PubMed and Scopus databases were conducted to identify original clinical studies analyzing molecular biomarkers in seminal fluid from patients with prostate or testicular tumors. For each study, data were extracted on biomarker types, cohort characteristics, analytical methods and diagnostic performance. Results: Forty-two eligible studies were included, covering multiple biomarker classes. Most were observational, single-center investigations classified as level 3b evidence. Across the different types of biomarkers, seminal fluid was associated with tumor-associated molecular changes. Alterations in the concentration, fragmentation and methylation patterns of cell-free DNA (e.g., GSTP1, RARβ2, LGALS3 and OCT3/4) distinguished malignant from benign conditions with sensitivities of up to 80-100%. RNA-based markers, including microRNAs, small non-coding RNAs, and tRNA fragments, showed improved performance in several studies, with multimarker models achieving areas under the curve (AUCs) of 0.85-0.93. Proteomic analyses identified high-specificity candidates such as TGM4, AMACR, PROS1 and DKK3. Metabolomic profiling further strengthened the diagnostic potential; reduced seminal citrate outperformed prostate-specific antigen (AUC 0.748 vs. 0.548), and reproducible shifts in amino acid and lipid profiles were observed in testicular tumors. However, substantial heterogeneity in study design, patient selection, and analytical platforms was observed. Risk of bias varied, and large prospective validation cohorts were lacking. Conclusions: Current evidence suggests that seminal fluid contains molecular signals associated with tumors that could be used for diagnosis. However, the available data are predominantly exploratory and methodologically heterogeneous. Before seminal fluid-based biomarkers can be considered for routine clinical implementation, robust prospective studies with standardized protocols are required.