Increased gene copy number of HER2 and concordant protein overexpression found in a subset of eyelid sebaceous gland carcinoma indicate HER2 as a potential therapeutic target

Purpose To identify crucial molecular alterations of receptor tyrosine kinases that can be used as potential therapeutic targets for eyelid sebaceous gland carcinoma (SbGC). Methods The expression levels of HER2, EGFR, C-MET, and FGFR1 were determined by immunohistochemistry (IHC). The copy numbers of the HER2, EGFR, C-MET, and FGFR1 genes were assessed by fluorescence in situ hybridization. The IHC and molecular results were correlated with the clinical parameters. Results A total of 49 patients with eyelid SbGC were included in this study. HER2, EGFR, C-MET, and FGFR1 protein expression was detected in 8 of 44 (16.3 %), 8 of 45 (17.8 %), 3 of 35 (8.6 %), and 0 of 45 patient samples, respectively. Increased copy numbers of the HER2 gene were found in 5 of 42 patient samples (11.9 %), including two with amplification (4.7 %) and three with polysomy (7.2 %). EGFR amplification was found in 2 of 33 (6.1 %) and FGFR1 amplification in 4 of 33 patient samples (12.1 %; high-level amplification in one and low-level amplification in three). None of the samples examined exhibited C-MET amplification. Gene copy number of the HER2 gene was correlated with its protein expression (p < 0.0001), whereas copy number of EGFR, C-MET, or FGFR1 was not correlated with protein expression. However, samples with EGFR amplification also exhibited a high level of expression of this protein. Conclusions Extra copies of the HER2, EGFR, and FGFR1 genes were identified in a 6-12 % of eyelid SbGCs. A high level of concordant HER2 expression detected by immunohistochemistry can be predictive of a copy number gain of the HER2 gene. Our data suggest that the therapeutic targeting of HER2 might benefit for a subset of patients with periocular SbGCs.