Chronic graft-versus-host disease: Update on pathobiology, biomarkers, and evolving treatment algorithms.

Chronic graft-versus-host disease (cGVHD) remains the leading cause of late non-relapse mortality and long-term disability after allogeneic hematopoietic cell transplantation (allo-HCT), affecting 30-70% of long-term survivors. Despite its substantial morbidity and the toxicities associated with prolonged corticosteroid use, therapeutic advances have accelerated considerably. This review synthesizes current mechanistic insights and clinical evidence within the framework of the well-established three-phase pathogenesis model of cGVHD. Phase 1 (early inflammation) involves tissue injury and innate immune activation; Phase 2 (months 2-12) is characterized by impaired central and peripheral tolerance with aberrant B- and T-cell responses; Phase 3 (>1 year) features macrophage-driven fibrosis and end-organ damage. Recognizing that these phases are conceptual and frequently overlap in clinical practice, we explore the alignment of contemporary biomarkers with each phase-ST2/CXCL9 (Phase 1), BAFF/autoantibodies (Phase 2), and MMP3/TGF-β (Phase 3)-and discuss how FDA-approved agents (ibrutinib, ruxolitinib, belumosudil, axatilimab) may target phase-specific pathways. A conceptual, risk-stratified treatment algorithm is proposed to link pathobiology to clinical decision-making, with the important caveat that biomarker-guided selection remains investigational and currently complements, rather than replaces, comprehensive clinical assessment. Notably, the adoption of prophylaxis and upfront strategies to prevent cGVHD has substantially reduced cGVHD incidence in modern cohorts.