The signaling pathways and molecular targets that may be harnessed for molecular imaging in cancer are glucose metabolism [255], integrin αvβ3 [271], melanocortin-1 receptor [332], PD-1/PD-L1 axis [272], and hence several other biochemical and molecular markers related to immune response and angiogenesis reside in the area of preclinical development [360]. This evidence concerns the gene PDCD1 and cancer.