Lo et al. BMC Cancer 2012, 12:235 http://www.biomedcentral.com/1471-2407/12/235 Page 10 of 13 Figure 3 DNA copy number validation by qPCR (A) and mRNA expression validation by RT-qPCR (B) of four candidate genes in clinical samples. The Y-axis is the mean DNA dosage ratio (A) or mean mRNA expression ratio (B) between candidate gene and the internal control gene in all samples analyzed. The P values of comparison between normal (N) and tumor (T) samples for each gene is as indicated. unique in Asian lung cancer, whereas Caucasian lung cancer was addictive to cell surface receptor linked sig- nal transduction and G-protein coupled receptor protein signaling pathways (Figure 1A-B). Genes involved in these pathways warrant further studies. This study found several candidate genes which are located in the common chromosome alteration regions in both Asian and Caucasian, such as PAFAH1B1 gene on 17p13.3. In array-CGH data, chromosome region 17p13.3 harboring PAFAH1B1 showed gain of copy number in 60% of Asian and 70% of Caucasian patients (Table 1). In addition, PAFAH1B1 DNA copy number and mRNA expression level in tumor tissues was sig- nificantly higher than that of the matched-normal tissues in both Asian and Caucasian lung cancer patients (Figure 3). The frequency of PAFAH1B1 protein overex- pression was 68% in Asian and 70% in Caucasian (Figure 4). Interestingly, chromosome region 17p13.3 harboring PAFAH1B1 gene also demonstrated associ- ation with advanced tumor stage in array-CGH data (Table 3A). Overexpression of PAFAH1B1 mRNA was found in 59.1% of early-stage and 78.3% of late-stage lung cancer patients of Asian descent (Additional file 6: Table S5), suggesting that the alteration of PAFAH1B1 gene may be involved in both tumor initiation and pro- gression. More patients will be analyzed to clarify its tumorigenic role. We also found several candidate genes showing differ- ent alteration frequency between Asian and Caucasian patients, such as ARHGAP19 and FRAT2. These two closely located (within a 39.8 kb region at 10q24.1) can- didate genes, showed alteration frequency of 57.5% with gain of gene copy number in Asian (Table 1A), whereas the alteration frequency was only 20% in Caucasian