STEAP is expressed in metastatic prostate cancer samples; in particular, STAMP1/STEAP2 (3) and STAMP2/STEAP4 (4) are expressed in the androgen receptor-positive prostate cancer cell line LNCaP, and androgen receptor-mediated regulation of STAMP2 has previously been demonstrated (4). This evidence concerns the gene STEAP4 and Familial prostate cancer.