GZMB and neoplasm: Ex vivo immunofluorescence staining confirmed the comparably low granzyme B secretion on day 0 in the 2 tumor models; however, considerably higher granzyme B secretion was observed in the MC38 compared with the 4T1 tumors on day 6 (Figure 4J), which was consistent with the 68Ga-grazytracer PET imaging results.