PET with intravenous 64CuCl2 was evaluated in athymic mice bearing hepatoma xenografts, with hCTR1 as its putative molecular target, and later in mice bearing various human cancer xenografts including prostate, hepatocellular carcinoma, melanoma, head and neck, glioblastoma, and breast cancers (17,18), showing promise particularly in anatomic regions with low background 64CuCl2 uptake such as the pelvic area and brain. Here, SLC31A1 is linked to cancer.