Therefore, our work provides additional evidence that CTR1 expression may not be universally increased in cancer [35], and that further investigation is required to establish if CTR1 overexpression indeed underlies increased uptake of 64CuCl2 in cancer tissues and if hCtr1 could be used as an appropriate biomarker to predict this compound’s efficacy and monitor therapy in a clinical setting. This evidence concerns the gene SLC31A1 and cancer.