In vivo, a large excess (100X) of non-radiolabeled apelin ligand enabled a significant 87.1 ± 0.9% reduction of [68Ga]Ga-AP747 PET tumor-to-muscle ratios compared to non-blocked conditions in T84 tumors (1.02 ± 0.31 and 7.93 ± 2.17, respectively, *P = 0.023, n = 3; Shapiro–Wilk normality tests: [68Ga]Ga-AP747 group: P = 0.1100; [68Ga]Ga-AP747 “blocking” group: P = 0.3365) (Fig. 3c, e). Here, APLN is linked to neoplasm.