NKX3.1 is a homeobox gene which exhibits prostate- and testis-specific expression. Loss of NKX3.1 expression has been implicated in prostate development and tumorigenesis. NKX3.1 expression is dramatically down-regulated in testicular cancer of germ cell origin. Results suggest that NKX3.1 is essential for normal testis function and that its loss of expression is highly associated with the invasive phenotype of testicular germ cell tumors.