GZMB and neoplasm: While the current biomarkers (e.g., PD-L 1 expression, CD 8 + T-cell density) are limited by spatial and temporal heterogeneity [1,10,11,12], our results demonstrate that granzyme B PET provides a dynamic, functional assessment of T-cell cytotoxicity—as evidenced by higher TBR values predicting subsequent substantial tumor regression.