Molecular, immunohistochemical and morphologic analysis of urothelial carcinoma with ERBB2/ERBB3 mutations

Abstract

<h3>Background</h3> Aberrations in ERBB2 (both amplification and mutations) and ERBB3 represent a novel therapeutic avenue for HER2/HER3-targeted therapy. A minority of urothelial carcinoma (UC) is known to have ERBB2 amplification but little is known about ERBB2 and ERBB3 mutations in this disease. We identified a cohort of UC with ERBB2/ERBB3 mutations using a next generation sequencing platform and performed detailed histopathologic evaluation and immunohistochemistry for HER2. <h3>Methods</h3> A total of 138 UC cases were studied. Frozen tumor tissue and matching germline DNA from peripheral blood were analyzed using a targeted, deep-sequencing assay designed to identify point mutations, indels, and copy number alterations in 300 cancer-associated genes, including ERBB2 and ERBB3. HER2 IHC was performed on the confirmed mutant UCs and on 14 randomly selected cases from the cohort that were without ERBB2/ERBB3 mutations or amplification. <h3>Results</h3> ERBB2 mutations were identified in 15 cases (11%). There were 14 missense mutations and one frameshift mutation. Two HER2 mutant UCs also exhibited ERBB2 amplification. ERBB3 mutations were identified in 17 cases (12%), all of which were missense mutations. Three cases had concurrent ERBB2 and ERBB3 mutations (2%).The majority of the ERBB2/ERBB3 mutant tumors did not exhibit HER2 overexpression as determined by intense and diffuse membranous staining by IHC. Only 4 mutant cases had 3+ staining, 2 of which also had HER2 amplification. Many tumors with wild-type ERBB2 and ERBB3 expressed HER2 at variable intensity but none as 3+. <h3>Conclusions</h3> Mutations in ERBB2 and ERBB3 are present in a significant minority of urothelial carcinoma and may represent targets for anti-HER2 and anti-HER3 therapy. HER2 immunohistochemistry is not a sensitive method for identifying tumors with ERBB2/ERBB3 mutations.