BACKGROUND: Activating, nonamplification ERBB2 mutations (ERBB2mut) are not detected by immunohistochemistry (IHC) or fluorescence in situ hybridization (FISH), but are detected by DNA sequencing and may predict clinical responses to human epidermal growth factor receptor (HER2)-targeted therapy. The authors queried 5605 advanced/metastatic breast cancers (mBC) to uncover the frequency of ERBB2mut genomic alterations. Clinical responses to anti-HER2 therapeutics were identified. METHODS: DNA was extracted from 40 mm of formalin-fixed paraffin-embedded (FFPE) sections. Comprehensive genomic profiling (CGP) was used to evaluate up to 315 genes (5923 mean coverage depth). Results were analyzed for base substitutions, short indels, copy number changes, and selected rearrangements. RESULTS: Of 5605 cases, 698 (12.5%) featured ERBB2 alterations, including 596 (10.6%) ERBB2 amplifications (ERBB2amp) and 138 (2.4%) ERBB2mut; 38 cases (0.7%) had co-occurring ERBB2amp and ERBB2mut. ERBB2mut predominantly affected the kinase (124 cases; 90%) or extracellular (15 cases; 11%) domains. Both primary BC (52 cases; 38%) and metastatic site biopsies (86 cases; 62%) were found to harbor ERBB2mut, which were distributed across carcinoma not otherwise specified (NOS) (69 cases; 50%), invasive ductal carcinoma (IDC) (40 cases; 29%), invasive lobular carcinoma (ILC) (27 cases; 20%), and mucinous mBC (2 cases; 1%). Genes commonly coaltered with ERBB2 were tumor protein 53 (TP53) (49%); phosphatidylinositol 3-kinase catalytic subunit alpha (PIK3CA) (42%); cadherin 1, type 1 (CDH1) (37%); MYC (17%); and cyclin D1 protein (CCND1) (16%). CDH1 mutations were enriched in ERBB2mut mBC (P<0.0006) and associated with recurrent mBC. Selected patients with ERBB2mut, without ERBB2amp, who responded to anti-HER2 targeted therapies are presented herein. CONCLUSIONS: Within this large series, 1.8% of cases harbored ERBB2mut, which are undetectable by standard-of-care IHC or FISH tests. Metastatic BC driven by ERBB2mut respond to anti-HER2 targeted therapies, and expanding clinical trials designed to detect ERBB2mut by CGP and optimize targeted treatments are warranted. Cancer 2016;122:2654-62. V C 2016 American Cancer Society.KEYWORDS: breast cancer, comprehensive genomic profiling, ERBB2, human epidermal growth factor receptor 2 [HER2]/neu, nextgeneration sequencing, short variants.
INTRODUCTIONThe ERBB2 gene encodes a transmembrane tyrosine kinase receptor that is a member of the epidermal growth factor receptor/ human epidermal growth factor receptor (HER) family of proteins.1 ERBB2 gene amplification has been identified in 10% to 34% of invasive breast cancers, is associated with HER2 (p185 neu) protein overexpression, and has been associated with increased cell proliferation, cell motility, tumor invasiveness, progressive regional and distant metastases, accelerated angiogenesis, and reduced apoptosis.2-4 ERBB2-driven breast cancer is more frequently associated with higher histologic grade, is more often negative for estrogen receptor (ER) and p...