The Invisible Barrier in Solid Tumors: Interstitial Transport Failure, Matrix Mechanics, and Ionic-Metabolic Adaptation: A Testable Systems-Physiology Hypothesis

Independent Working Paper, Version 1.0 (July 2026). This manuscript has not been peer reviewed and proposes no diagnostic or therapeutic protocol. Solid tumors are mechanically and physiologically abnormal tissues. Distorted vasculature, extracellular-matrix remodeling, solid stress, elevated interstitial pressure, impaired perfusion, and heterogeneous lymphatic function can restrict convection and diffusion, alter oxygen and metabolite exchange, and limit drug and immune-cell access. This established transport biology is here organized under the operational term “failed tissue logistics.” The proposed Invisible Barrier hypothesis asks whether these physical constraints are coupled to a second, incompletely integrated layer of ionic and metabolic adaptation. Human and preclinical 23Na magnetic-resonance studies show elevated total tissue sodium in breast tumors; ex vivo and mechanistic studies identify elevated intracellular Na+ and link Na+ influx and Na+/K+-ATPase workload to glycolytic flux and extracellular acidification. Separately, extracellular Mg2+ can regulate LFA-1-dependent CD8+ T-cell effector function. These findings support specific connections, but they do not establish that sodium accumulation, magnesium deficiency, or interstitial stasis initiates cancer. The central proposal is narrower: in selected adult solid tumors, matrix mechanics, transport failure, ionic workload, pH regulation, and metabolic adaptation may form a measurable, self-reinforcing phenotype that modifies treatment access and malignant behavior. The paper separates established evidence from extrapolation, specifies competing explanations, and defines tests capable of weakening or falsifying the model. No dietary, supplement, drainage, or anticancer intervention is inferred from the hypothesis.