Background Tumor epithelial barriers physically impede immune cell infiltration, causing immune exclusion and resistance to immune checkpoint inhibitors (ICIs). However, a simple, spatially quantifiable biomarker of epithelial barrier strength is lacking. In head and neck squamous cell carcinoma (HNSCC), HPV status is used as a surrogate for ICI response, but its association with true immune exclusion remains unclear.Methods Using Xenium and Visium spatial transcriptomics data from nine cancer types (pancreatic, lung, breast, colorectal, cervical, ovarian, HNSCC, skin melanoma, kidney, and acute lymphoblastic leukemia bone marrow), we defined a compact 8‑gene epithelial barrier signature (EpiBarrier), together with a stromal signature and an immune activity signature. Spatial niche clustering, pan‑cancer comparisons, and external immunotherapy cohort validation were performed to test whether high EpiBarrier regions exhibit low stromal and low immune activity. In HNSCC, we compared the signature with HPV status.Results In six epithelial cancer types (pancreatic, lung, breast, colorectal, cervical, ovarian), high‑EpiBarrier regions consistently showed significantly lower stromal scores (17–87% reduction) and lower immune activity scores (5–73% reduction) (all P < 0.05). In skin melanoma, high‑EpiBarrier cells corresponded to normal epidermal structures and also exhibited reduced stromal and immune activity (P = 8e‑27), confirming the signature’s specificity to genuine epithelial cells. Non‑epithelial tumors (kidney, ALL bone marrow) did not support the model or showed opposite trends. In HNSCC, the model outcome was independent of HPV status: HPV‑high samples could be immune‑excluded (model supported) or immune‑hot (model not supported), while HPV‑negative samples were immune‑excluded. An external ICI‑treated HNSCC cohort (GSE159067, n = 102) validated that EpiBarrier predicted overall survival (HR = 1.744, P = 0.0205) and moderately predicted treatment response (AUC = 0.702).Conclusions The 8‑gene epithelial barrier signature is a pan‑epithelial‑cancer, spatially quantifiable biomarker of immune exclusion, independent of HPV status, and predicts immunotherapy outcome. It offers a clinically translatable tool for patient stratification in epithelial‑derived malignancies.