Antibody-based detection of ERG rearrangements in prostate core biopsies, including diagnostically challenging cases: ERG staining in prostate core biopsies.

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