STEAP1 and prostate cancer: As a relatively new member of the STEAP family, STEAP4 was found to be increased in human prostate cancers compared with normal prostate tissues (Korkmaz et al., 2005; Jin et al., 2015), and is up-regulated in human colon cancer cells, predicting poor prognosis of patients with colon cancers (Xue et al., 2017).