ERBB2 (HER2) Testing in Non-Small Cell Lung Cancer (NSCLC)

Three types of HER2 alterations in NSCLC have been described: HER2 mutations, HER2 amplification, and HER2 protein overexpression. HER2 gene amplifications are found as de novo or acquired alterations, as one of the mechanisms responsible for acquired EGFR tyrosine kinase inhibitor resistance [1].

HER2 protein overexpression is characterized by an overabundance of HER2 proteins expressed on the cell surface that increases the formation of HER2-containing heterodimers, which lead to activation of several oncogenic signaling pathways [2]. In contrast to breast cancer in NSCLC, the correlation between HER2 amplification and HER2 protein overexpression is poor, suggesting distinct roles in tumorigenesis.

A wide range of somatic HER2 mutations is found across several malignancies, including NSCLC, further defining a distinct molecular subset that is typically mutually exclusive with other oncogenic drivers. HER2 mutations encompass many single- nucleotide variants (SNVs) or insertions and deletions that can occur in the extracellular, transmembrane, juxtamembrane and intracellular kinase domains. The functional implications of dysregulation largely depend on where the mutation is located [3].

The majority of HER2 mutations occur in exons 18–20 of the kinase domain as in-frame duplications or insertions, ranging from 3 to 12 base pairs [2,5]. The most common of these is the YVMA insertion-duplication variant involving an in-frame exon 20 insertion at codon 776, accounting for up to 90% of all HER2 mutations [2].

Less frequently observed mutations are SNVs or other insertions in exon 20 or other exons that affect the transmembrane and juxtamembrane domains [5]. The significant heterogeneity observed in HER2 alterations in NSCLC requires distinct methods for identification.

HER2 protein overexpression is commonly detected by immunohistochemistry (IHC). In contrast to breast and gastric cancers, positivity in NSCLC determined by scoring is not universally established and requires further investigation.

HER2 amplification refers to a copy number increase at a specific chromosome location relative to the whole chromosome and is primarily detected using fluorescence in situ hybridization (FISH). Alternatively, HER2 amplification can also be detected by next-generation sequencing (NGS), with the advantage of simultaneously detecting variants across numerous genes.

Reverse-transcription polymerase chain reaction (RT-PCR) is a common method used to detect HER2 mutations. The limitation of RT-PCR is its ability to only detect known and well-characterized mutations, and its inability to detect less common variants.

Oncomine Solutions are complete end-to-end NGS workflows, including bioinformatics, for precision oncology research. Requiring as little as 10 ng of DNA or RNA, Oncomine Solutions can generate results from limited tissue and small biopsies in as little as 24 hours.

Oncomine Solutions provide an ideal method for molecular profiling in NSCLC because of the ability to identify relevant variants in HER2, including exon 20 insertions, SNVs, and amplifications, with low input requirements, high sensitivity, and a short turnaround time.