Engrailed homeobox transcription factors as potential markers and targets in cancer.

Engrailed (En) is a member of the homeobox gene family, which encodes a homeodomain-containing transcription factor that is essential during early development. The only known site of normal adult Engrailed protein (EN) expression is in the nervous system, and it has been implicated in the development of both young-onset Parkinson's disease as well as autism. Over-expression of EN has been linked to tumour development in adults, particularly in breast, prostate, melanoma and ovarian cancers, and there is a growing interest in its role as a diagnostic and prognostic biomarker. It is hoped that further work may confirm associations between En expression and therapy-resistant, poor prognosis cancers, similar to that identified with other homeobox gene profiles.