Although 1 study in 5 cancer cell lines found no correlation of 64CuCl2 uptake with hCTR1 expression (measured by quantitative polymerase chain reaction) (19), others showed that hCTR1 knockdown in PC3 prostate cancer xenografts reduced 64Cu uptake from 7.21 to 4.02 percentage injected dose per gram (P < 0.001) (20) and hCTR1 overexpression in a MDA-MB-231 breast cancer model increased it from 2.58 to 5.37 percentage injected dose per gram (P < 0.05) (21). The gene discussed is SLC31A1; the disease is breast cancer.