Eestrogen receptor beta 5 (ERB5) is a splice variant of the nuclear receptor hormone ERbeta (ESR2), shown to exist in at least five isoforms (ERB1-ERB5). Although only the ERB1 variant appears fully functional, the remaining isoforms have been shown to form heterodimers with ERB1, thereby enhancing transcription. Immunohistochemical studies have revealed a ubiquitous expression of ERB5 in normal colorectal tissue, and to be present in all primary colorectal carcinomas studied (1). Studies also revealed the nuclear expression of ERB5 in the majority of breast carcinomas tested, with a possible association with improved patient survival (2).