Testing and Interpretation of Human Epidermal Growth Factor Receptor 2 Protein Expression and <i>ERBB2</i> Gene Amplification in Advanced Urothelial Carcinoma.

Abstract

The aim of this study was to assess the prevalence of human epidermal growth factor receptor 2 (HER2) protein expression and <i>ERBB2</i> gene amplification in a large cohort of tumor samples from patients with advanced urothelial carcinoma (UC). Testing was performed on formalin-fixed, paraffin-embedded tissue from commercially sourced primary advanced or metastatic UC using an anti-HER2/neu (4B5) rabbit monoclonal antibody immunohistochemistry (IHC) assay (detects HER2 protein) and HER2 dual in situ hybridization (DISH) DNA probe cocktail assay (detects <i>ERBB2</i> gene and the centromere of its residing chromosome 17). The HER2 clinical status was classified as HER2-zero (IHC 0), HER2-low (IHC 1+ or IHC 2+/DISH nonamplified), or HER2-positive (IHC 2+/DISH amplified or IHC 3+). Of the 2,024 UC samples, HER2 protein expression was IHC 0 for 962 (47.5%), IHC 1+ for 297 (14.7%), IHC 2+ for 498 (24.6%), and IHC 3+ for 267 (13.2%). The percentage of HER2-expressing tumors (IHC 1+, 2+, and 3+) was similar between primary (52.2%, 1,028/1,968) and metastatic UC samples (60.7%, 34/56; <i>P</i> = .26). The <i>ERBB2</i> gene was amplified in 235 cases (11.6%), including 2.7%/3.7%/9.6%/56.2% scored as IHC 0/1+/2+/3+, respectively. Overall, HER2 clinical status was HER2-zero for 962 UC tissue samples (47.5%; 95% CI, 45.4 to 49.7), HER2-low for 747 (36.9%; 95% CI, 34.8 to 39.0), and HER2-positive for 315 (15.6%; 95% CI, 14.0 to 17.2). We observed that more than 50% of 2,024 advanced UC tumors demonstrated some degree of HER2 protein expression detected using a standardized IHC method, whereas about 12% of specimens had <i>ERBB2</i> gene amplification, including about 3% of those scored as either IHC 0 or 1+. Continued development of optimized and standardized HER2 testing methods is warranted to identify patients with HER2-expressing UC who may benefit from novel HER2-targeting therapies.