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Six non-small cell lung cancer (NSCLC) cell lines (A-549, Ca-Lu-6, SK-Lu-1, Ca-Lu-1, SK-Mes-1 and LX-1) were studied to assess the presence of multiple concomitant alterations of different oncogenes (K-ras, bcl-2) and tumor suppressor genes (p53, Rb) in NSCLC. K-ras (exon 1) and p53 (exons 5-8) gene mutations were determined via a PCR-based-DGGE (Denaturing Gradient Gel Electro-phoresis) and by sequencing approach. Different mutations were found in the Ist exon of K-ras gene in 5 of 6 cell lines examined. Five of six cell lines contained K-ras mutations at codon 12 (A-549, SK-Lu-1, LX-1) or codon 13 (SK-Mes-1, Ca-Lu-1). In addition, 5 of 6 cell lines showed p53 mutations of exon 8 (SK-Mes-1, Ca-Lu-1 cod. 280; LX-1 cod. 273) or exon 6 (Ca-Lu-6 cod. 196; SK-Lu-1 cod. 193). In 4 of these cell lines, p53 protein nuclear expression was also confirmed with DO-7 mAb immunocytochemistry. Expression of cytoplasmic bcl-2 protein, by anti-bcl-2 mAb flow cytometric analysis, was found in A-549, Ca-Lu-1, SK-Lu-1, SK-Mes-1 cell lines. In contrast, RT-PCR analysis of Rb gene could not identify any change in the cell lines examined. In conclusion, most NSCLC cell lines tested displayed concomitant multiple oncogene/tumor suppressor gene alterations.