Background: NKX3.1 is an androgen-regulated homeobox gene specifically expressed in prostate cells. It is mainly localized in the prostatic epithelium, but is also present in the testis, ureter, and bronchial mucous glands of the lung. As a transcription factor, it has a key role in prostate development and tumor suppression. It is a negative regulator of epithelial cell growth in prostate tissue. NKX3.1 has a high sensitivity and specificity in tumors of prostate epithelial origin. It is not expressed in bladder cancer and nephrogenic tumors and can be used for the differential diagnosis of prostate cancer.