Host Immune Response Signatures for Early Breast Cancer Detection: Biological Rationale, Current Evidence, and Clinical Translation

Early breast cancer may induce a systemic immune response before abundant tumor-derived material reaches the circulation, creating a potential source of amplified liquid-biopsy biomarkers. However, the extent to which host-response signatures can support early detection or population screening before diagnosis remains uncertain. This structured narrative review examines the biological basis, analytical platforms, evidence, clinical roles, and translational requirements of circulating autoantibodies, leukocyte transcriptomic and epigenetic profiles, immune-cell phenotypes, adaptive immune-receptor repertoires, soluble mediators, extracellular vesicles, and integrated multi-omics. PubMed/MEDLINE and citation networks were searched through August 31, 2026 using a predefined diagnostic review framework. Evidence was organized by intended use, sample timing, comparator spectrum, and validation maturity, with appraisal informed by established diagnostic-accuracy and prediction-model standards. Proof-of-concept estimates include a mean area under the curve of 0.96 for a machine-learning T-cell receptor model in 98 women, 80.8% sensitivity and 61.6% specificity for a 28-autoantibody panel, and an external-validation area under the curve of 0.951 for a 20-analyte proteome-metabolome model involving 662 participants. These estimates are not directly comparable: most derive from retrospective case-control or diagnostic cohorts with established cancer, healthy or benign comparators, post-diagnosis sampling, data-driven thresholds, and limited independent validation. Consequently, discrimination between known cases and controls must not be equated with detection of occult disease or population screening utility. Breast-specific prediagnostic evidence and screening validation remain sparse. Host-response signatures are therefore best considered investigational, complementary biological sensors rather than replacements for mammography. Their most plausible future roles include triage after equivocal imaging, enrichment for supplemental imaging, and longitudinal surveillance in high-risk populations. Translation requires prospective prediagnostic cohorts, representative benign and inflammatory controls, locked algorithms, high-specificity performance, calibration at screening prevalence, external validation, subgroup fairness, reproducibility, and evidence that testing improves cancer yield or stage distribution without unacceptable false-positive procedures, overdiagnosis, cost, or inequity.