Expression levels of TRAIL-R, DR5, DcR1 and DcR2 are not significantly different among normal (NOM), immortalized (16B), premalignant (OPM), and malignant primary (Iry) and metastatic (Met) oral epithelial cells. Relative RNA expression levels of TRAIL-R were determined using Affymetrix U133A oligonucleotide microarrays and their signal intensities were calculated using the Affymetrix MAS 5.0 probe level algorithm. Phenotypic-specific gene expression values for DR5, DcR1 and DcR2 genes were calculated by averaging signal intensities across sample replicates for cell lines belonging to each phenotypic group. The mRNA levels of DR5 are significantly higher than the DcR1 and DcR2 mRNA levels in these cell lines. The DNA microarray chips used in this study did not have the probe sets for DR4. NOM: Normal oral epithelial cells; 16B: Immortalized normal oral epithelial cells; OPM: Average target intensities of premalignant cell lines MSK-Leuk1 and MSK-Leuk2; 16BTu: tumorigenic cell line derived from HOK-16B; Iry: Average target intensities of primary OSCC cell lines 1386TU, 686Tu and 101A. Met: Average target intensities of metastatic OSCC cell lines 1386Ln and 686Ln.