Prevalence, clinicopathologic associations, and molecular spectrum of ERBB2 (HER2) tyrosine kinase mutations in lung adenocarcinomas

Abstract

Purpose: Activating mutations in the tyrosine kinase domain of HER2 (ERBB2) have been described in a subset of lung adenocarcinomas (ADCs) and are mutually exclusive with EGFR and KRAS mutations. The prevalence, clinicopathologic characteristics, prognostic implications, and molecular heterogeneity of HER2-mutated lung ADCs are not well established in U.S. patients.

Experimental design: Lung ADC samples (N = 1,478) were first screened for mutations in EGFR (exons 19 and 21) and KRAS (exon 2), and negative cases were then assessed for HER2 mutations (exons 19-20) using a sizing assay and mass spectrometry. Testing for additional recurrent point mutations in EGFR, KRAS, BRAF, NRAS, PIK3CA, MEK1, and AKT was conducted by mass spectrometry. ALK rearrangements and HER2 amplification were assessed by FISH.

Results: We identified 25 cases with HER2 mutations, representing 6% of EGFR/KRAS/ALK-negative specimens. Small insertions in exon 20 accounted for 96% (24/25) of the cases. Compared with insertions in EGFR exon 20, there was less variability, with 83% (20/24) being a 12 bp insertion causing duplication of amino acids YVMA at codon 775. Morphologically, 92% (23/25) were moderately or poorly differentiated ADC. HER2 mutation was not associated with concurrent HER2 amplification in 11 cases tested for both. HER2 mutations were more frequent among never-smokers (P < 0.0001) but there were no associations with sex, race, or stage.

Conclusions: HER2 mutations identify a distinct subset of lung ADCs. Given the high prevalence of lung cancer worldwide and the availability of standard and investigational therapies targeting HER2, routine clinical genotyping of lung ADC should include HER2.

Conflict of interest statement

Conflict of interest: none to disclose

©2012 AACR.

Figures

Figure 1. Summary of ERBB2 / HER2 mutations identified in the current study (26 mutations, 25 patients)

(2A) Schematic organization of ERBB2 kinase domain and detailed structure of the proximal region of Exon 20. Open black arrows flank the beginning and the end of exon 20. Solid black arrows mark the specific locations of the identified mutations. Mutation hotspot is demarcated by the box. 2B. Spectrum of mutations - Detailed description of all mutations identified. Insertion sequences are demarcated by the box; Black cross marks the point mutations.

Figure 2

Kaplan-Meier curve for overall survival in patients with advanced stage (IIIB/IV) disease. The overall survival of the HER2 cohort was not statistically different from the other molecularly defined cohorts.

Figure 3. Representative case harboring the most common ERBB2 mutation

A775_G776insYVMA. (3A) Morphologically, this tumor showed a mixed phenotype with papillary, micropapillary and solid components. (3B) Standard sequencing (reverse) shows further characterization of the mutation as A775_G776insYVMA (2325_2336ins12 [ATACGTGATGGC]), bottom tracing. The arrow marks the beginning of the insertion sequence. Top tracing demonstrates the reverse WT sequence for comparison (3C) ABI tracing of the sizing assay shows a heterozygous 12bp insertion (arrow); asterisk marks the adjacent wild-type peak (*). This case was concurrently tested for indels in exon 19 and 20 of EGFR using a multiplex assay and illustrates the mutually exclusive nature of these mutations.

Figure 4

Positions of the HER2 exon 20 insertions identified in the present study and comparison with the spectrum of EGFR exon 20 insertion mutations identified at our institution over a 3 year period. Insertions in HER2 show significantly less heterogeneity compared to EGFR with over 80% of HER2 alterations being represented by the A775_G776insYVMA.