Using a mouse colon carcinoma model, Yoshii et al. discovered that [64Cu][Cu(ATSM)] indeed preferentially accumulates in regions of tumors with high expression of CD133+, which are characterized as cancer stem cells (CSCs) and enriched under hypoxia due to survival advantages, as well as promoted self-renewal ability through the activation of the hypoxia inducible factor-1α (HIF-1α) [20–22]. Here, HIF1A is linked to cancer.