Eukaryotic elongation factor 1 alpha 2 (eEF1A2) encodes an isoform of the alpha subunit of the elongation factor 1 complex and is responsible for the enzymatic delivery of aminoacyl tRNA to the ribosome. Our proteomic analysis has identified eEF1A2 as one of the proteins expressed during malignant progression from adenocarcinoma in situ (AIS) to early invasive lung adenocarcinoma. The expression level of eEF1A2 in 175 lung adenocarcinomas was examined by immunohistochemical staining in relation to patient prognosis and clinicopathological factors. Quantitative PCR analysis and fluorescence in situ hybridization (FISH) were performed to evaluate the amplification of the eEF1A2 gene. Relatively high expression of eEF1A2 was observed in invasive adenocarcinoma (39/144 cases) relative to minimally invasive adenocarcinoma (1/10 cases) or AIS (0/21 cases). Among invasive adenocarcinomas, solid-type adenocarcinoma (15/32 cases, 47%) showed higher expression than other histological subtypes (23/92, 25%). Patients with eEF1A2-positive tumors had a significantly poorer prognosis than those with eEF1A2-negative tumors. Of the five tumors that were eEF1A2-positive, two cases showed amplified genomic eEF1A2 DNA, which was confirmed by both qPCR and FISH. These findings indicate that eEF1A2 overexpression occurs in the course of malignant transformation of lung adenocarcinomas and is partly due to eEF1A2 gene amplification.