Importance of HOX genes in normal prostate gland formation, prostate cancer development and its early detection.

The aims of this paper were to review the published literature on the role of HOX genes in the development of the normal prostate gland and in prostate cancer and to discuss the potential role of the HOX family member, Engrailed-2 (EN2), as a diagnostic test of PCa. Hox genes were first described in the fruit fly Drosphila melanogaster, where they specify the body plan and control the formation of body segments. They belong to a family of homeodomain-containing transcription factors that determine cell and tissue identity during normal embryonic development. They have been shown to be re-expressed by several different types of cancers. Studies have shown that different Hox genes are responsible for the development of the separate lobes of the prostate gland, the seminal vesicles and the epididymis. All HOX13 paralogues are expressed in the adult human prostate, suggesting the possibility of similarities between the function and expression of HOX genes within urological structures at similar anterior-posterior positions. The oncogenic and tumour suppressor signalling pathways associated with PCa converge on the HOX gene network, which ultimately controls gene expression, affecting tumour formation and metastatic progression. The Engrailed genes (EN1 and EN2) from the HOX gene family show a very high degree of functional conservation during embryonic development. Urinary EN2 is being investigated as a potential diagnostic marker of early PCa. It is secreted into the urine by PCa cells but not by normal prostatic tissue. A recent study has shown an association between urinary EN2 levels and cancer volume in radical prostatectomy specimens. The ability to predict tumour volume could inform the treatment decision-making process for patients with localized PCa choosing between active surveillance and radical treatment options.