Clinical ERG break-apart fluorescence in situ hybridization assay: practical utility and lessons from an 8-year tertiary institution experience.

Abstract

ERG gene fusions are present in up to 60% of localized prostate cancer and up to 45% of metastatic prostate cancer. Fluorescence in situ hybridization (FISH) assays can detect the vast majority of ERG gene fusions and help confirm prostatic origin. We reviewed clinical ERG FISH assays performed at our tertiary institution by our in-house consult services between 2016 and 2024 where prostatic adenocarcinoma was in the differential diagnosis. We summarized clinical information, immunohistochemistry results (including ERG), and ERG FISH status in a cohort of 15 consecutive clinical ERG FISH assays performed for 14 patients in whom a diagnosis of prostatic adenocarcinoma was considered. ERG FISH testing was positive in 7 of 15 (46.7%) cases, indeterminate in 1 of 15 (6.7%) cases, and negative in 7 of 15 (46.7%) cases. In 6 of 7 (85.7%) positive cases, the ERG FISH-positive result supported prostatic origin in metastatic (n = 4) or undifferentiated (n = 2) disease. Use of clinical ERG FISH assays may help confirm prostatic origin in the setting of localized or metastatic carcinoma showing poor differentiation or transdifferentiation and thus help determine the correct diagnosis and direct appropriate clinical management for such patients.