XAF1 mRNA is expressed at low or undetectable levels in most cancer cell lines, and transcriptional down-regulation in tumour cells as opposed to corresponding normal tissues and has been shown to occur at different frequencies in gastric adenocarcinomas, colorectal cancer, urothelial carcinomas, malignant melanomas, clear-cell renal cell carcinomas [8,13-16,31], non-small cell lung cancer, bladder cancer and B chronic lymphocytic leukemia [15,32,33]. This evidence concerns the gene XAF1 and non-small cell lung carcinoma.