Fusions of androgen-regulated genes and v-ets erythroblastosis virus E26 oncogene homolog (avian) (ERG) occur in ~50% of prostate cancers, encoding a truncated ERG product. In prostatectomy specimens, ERG-rearrangements are >99% specific for prostate cancer or high grade prostatic intraepithelial neoplasia (HGPIN) adjacent to ERG-rearranged prostate cancer by fluorescence in situ hybridization (FISH) and immunohistochemistry (IHC).
To evaluate ERG staining by IHC on needle biopsies, including diagnostically challenging cases.
Biopsies from a retrospective cohort (n=111) enriched in cores requiring diagnostic IHC and a prospective cohort from all cases over 3 months (n=311) were stained with an anti-ERG antibody (clone EPR3864).
Amongst evaluable cores (n=418), ERG staining was confined to cancerous epithelium (71/160 cores, 44%), HGPIN (12/68 cores, 18%) and atypical foci (3/28 cores, 11%), with staining in only 2/162 (1%) cores diagnosed as benign. ERG was expressed in ~5 morphologically benign glands across 418 cores, and was uniformly expressed by all cancerous glands in 70/71 cores.
ERG staining is more prostate cancer-specific than alpha-methylacyl-CoA racemase (AMACR), and staining in an atypical focus supports a diagnosis of cancer if HGPIN can be excluded. Thus, ERG staining shows utility in diagnostically challenging biopsies and may be useful in molecularly subtyping prostate cancer and risk stratifying isolated HGPIN.