Fluorescence in situ hybridization gene amplification analysis of EGFR and HER2 in patients with malignant salivary gland tumors treated with lapatinib

BACKGROUND: Gene amplification status of the epidermal growth factor receptor (EGFR) and the human epidermal growth factor receptor 2 (HER2) were analyzed and correlated with clinical outcome in patients with progressive malignant salivary glands tumors (MSGT) treated with the dual EGFR/Her2 tyrosine kinase inhibitor lapatinib. METHODS: Fluorescence in situ hybridization (FISH) analysis for both EGFR and HER2 gene amplification was performed successfully in the archival tumor specimens of 20 patients with adenoid cystic carcinomas (ACC) and 17 patients with non-ACC, all treated with lapatinib. RESULTS: For ACC, no EGFR or HER2 amplifications were detected. For non-ACC, no EGFR gene amplifications were detected but 3 patients (18%) were HER2 amplified and all had stained 3+ for both EGFR and HER2 by immunohistochemistry (IHC) in their archival specimens. Two of these patients had time-to-progression (TTP) durations of 8.3 months and 18.4 months, respectively. Interestingly, patients with low and high HER2/chromosome-specific centromeric enumeration probe (CEP) 17 ratio had a prolonged TTP than those with moderate ratios for both ACC and non-AAC subtypes. CONCLUSIONS: HER2 to CEP17 FISH ratio may predict which patients with MSGT have an increased likelihood to benefit from lapatinib. The finding of HER2:CEP17 ratio as a predictive marker of efficacy to lapatinib warrants further investigation.