Microenvironment-defined priority pathways shape ICD-driven abscopal responses

While radiotherapy excels at local tumor control, it seldom orchestrates durable systemic immunity in the context of metastatic disease. The abscopal effect, the regression of non-irradiated distant lesions following focal irradiation, remains a clinical rarity rather than a predictable or robust consequence of monotherapeutic radiotherapy. Clinical manifestations of this phenomenon predominantly emerge within the framework of combinatorial radio-immunotherapy, specifically alongside immune checkpoint blockade, rather than as a byproduct of radiotherapy in isolation. This clinical reality underscores that radiotherapy-induced immunogenic cell death (ICD), though mechanistically pivotal, is rarely self-sufficient in catalyzing systemic antitumor immunity. We contend that the variability of the abscopal response cannot be ascribed solely to the presence or magnitude of radiotherapy-induced ICD; rather, it hinges decisively on how these ICD signals are "interpreted" across heterogeneous tumor microenvironments (TMEs). We propose a "priority pathway": a functionally dominant, TME-dictated axis of ICD signaling that orchestrates immune cell polarization, infiltration dynamics, and the overall trajectory of the antitumor response. Under this paradigm, uniform ICD signals, encompassing calreticulin exposure, ATP release, HMGB1 signaling, and cGAS-STING activation, yield profoundly divergent outcomes, contingent upon stromal architecture, myeloid landscapes, vascular integrity, and metabolic constraints. We present testable predictions and delineate the dynamic, temporal shifts in post-irradiation pathway dominance, offering a mechanistic rationale for the heterogeneity and transience of the abscopal effect. We synthesize these insights into an investigational precision strategy designed to remodel the TME and augment ICD signaling in a phased manner, thereby breaching immunosuppressive barriers, potentiating T-cell-mediated systemic immunity, and enhancing the reproducibility of abscopal responses in radio-immunotherapy. These propositions are intended to catalyze future preclinical and clinical inquiry, serving as a hypothesis-generating framework rather than a set of established clinical doctrines.