XAF1 and cancer: XAF1 mRNA is expressed at low or undetectable levels in most cancer cell lines, and transcriptional down-regulation in tumour as opposed to corresponding normal tissues has been shown to occur at different frequencies in gastric adenocarcinomas, colorectal cancer, urothelial carcinomas, malignant melanomas and also clear-cell renal cell carcinomas [17,18,21,28-30].