Utility of ERG Immunohistochemistry for Evaluation of Lymphovascular Invasion in Testicular Germ Cell Tumors: A Retrospective Pilot Study.

Lymphovascular invasion (LVI) of testicular germ cell tumors (GCT) is an important stage-determining variable in the evaluation of radical orchiectomy specimens. ERG endothelial cell expression, as detected by immunohistochemistry (IHC), robustly highlights lymphovascular spaces, and thus, we sought to assess the utility of ERG IHC for evaluation of GCT LVI. Hematoxylin and eosin (H&E) slides from a retrospective cohort of 25 GCT radical orchiectomy specimens (emanating from a parent cohort of 159 radical orchiectomy GCT cases identified between 2003 and 2013) were reviewed, and sections with foci of positive or equivocal LVI were identified. ERG IHC was performed on sections off the surface of corresponding paraffin tissue blocks. All foci were then rescored as positive, equivocal, or negative for LVI based on ERG endothelial cell expression. Twenty-three and 13 foci were positive or equivocal for LVI by H&E staining, respectively. Among the H&E positive LVI foci, 20 (87%) were ERG IHC positive, whereas of the H&E equivocal LVI foci, 5 (38%) were ERG IHC positive, 3 (23%) were ERG IHC negative, and 2 (15%) were ERG IHC equivocal; all other foci were lost for evaluation. Overall, ERG IHC helped resolve the LVI status of 61% of foci deemed equivocal for LVI by H&E staining only. Although ERG IHC is useful in confirming definitive LVI status in a subset of GCT cases, the overall clinical impact of ERG IHC is limited for H&E equivocal LVI foci in this specific retrospective patient cohort. Overall, in carefully selected clinical scenarios, these data suggest a supportive role for ERG IHC in evaluation of GCT LVI in radical orchiectomy specimens.