The STEAP family contains four members, named STEAP1–4, all of which have in common a six transmembrane domain with the COOH- and N-terminals located in the cytosol. STEAP1 was the first member of the STEAP family to be identified and has been widely studied as a gene related to cancer progression. STEAP1 was previously predicted not to promote iron and cooper reduction or uptake mainly due to the lack of the N-terminal NADPH-binding F420H2: NADP+ oxidoreductase domain unlike other STEAP members. However, a recent study revealed that STEAP1 exhibits cellular ferric reductase activity by fusing to the intracellular NADPH-binding domain of STEAP4. These findings can ultimately contribute to the development of STEAP1 targeted therapy. In contrast, the pathological functions of STEAP1 in cancer still need further investigation.