In this multicenter study, we systematically evaluated programmed cell death ligand 1 (PD-L1) expression (using tumor proportion score, TPS, and combined positive score, CPS) and cluster of differentiation 8-positive (CD8<sup>+</sup>) tumor-infiltrating lymphocyte (TIL) infiltration in the largest cohort to date of pathologically confirmed pure IMAs (<i>n</i> = 312), supported by single‐cell transcriptomic analysis. Here, CD274 is linked to neoplasm.