STEAP1 and prostate cancer: This protein, which was discovered in 1999 in an animal model of transplanted prostate cancer, is primarily expressed at the prostatic secretory epithelial cell–cell junction and named for its six potential transmembrane regions.4 Considering that the transmembrane region is flanked by hydrophilic amino and carboxyl terminals, STEAP may support a set of functions similar to those of ion channel and transporter proteins.5 The STEAP protein family consists of five members, namely, STEAP1, STEAP1b, STEAP2, STEAP3, and STEAP4.