OBJECTIVE To explore epidermal growth factor receptor (EGFR) and HER2 gene status, to assess the correlation between EGFR and HER2 gene status, and to investigate the role of copy number increase and amplification of EGFR gene and HER2 gene in the tumorigenesis and disease progression of non-small-cell lung cancer. METHODS Using Path Vysion kit and LSI EGFR SpectrumOrange/CEP7 Spectrum Green probes, EGFR gene and HER2 gene status were evaluated by fluorescence insitu hybridization (FISH) using formalin-fixed, paraffin-embedded samples from 31 patients with non-small-cell lung cancer, including 20 adenocarcinomas, 2 squamous cell carcinomas, 2 large cell carcinoma, 4 bronchoalveolar carcinomas and 3 adenosquamous carcinomas. The correlation between EGFR and HER2 gene status was analyzed. RESULTS Six of thirty-one carcinomas showed EGFR gene amplification. Of 25 cases without EGFR gene non-amplification, four tetrasomy and 5 polysomy were detected. Overall, 15 out of 31 carcinomas demonstrated either EGFR gene copy number increase or gene amplification (15/31). HER2 gene amplification was seen in 2 of the 31 cases. Four trisomy, one tetrasomy and nine polysomy cases were found in 29 tumors that had no HER2 gene amplification. Overall, 16 of 31 cases showed either HER2 gene copy number increase and/or amplification (16/31). Synchronous EGFR and HER2 gene numerical changes, i.e. gene copy number increase and gene amplification, were found in 12 of 31 cases (12/31), and almost all such patients had either clinical stage III or IV tumor. EGFR gene numerical changes significantly correlated with HER2 gene abnormality (chi(2)(Adj) = 7.3045, P = 0.0069). CONCLUSIONS EGFR or HER2 copy number increase is much more frequent than gene amplification in no-small-cell lung cancer. Our data based on gene alterations indicate, for the first time, that there is a significant correlation between EGFR alterations and HER2 abnormalities. Both genes are involved in the tumorigenesis and development of lung cancer. EGFR/HER2 dimer is one of the predominant heterodimerization types in lung cancer. The interactions between EGFR and HER2 may play a rule in the progression of non-small-cell lung cancer.