GAPDH and gastric cancer: The best single reference gene for each group is as follows; 'non-stomach cancer cell lines' - GAPDH (0.036), 'stomach cancer cell lines' - B2M (0.014), 'normal stomach tissues' - RPL29 (0.028), 'tumor stomach tissues' - RPL29 (0.028), 'all stomach tissues' - RPL29 (0.032) and 'all stomach cell lines and tissues' - ACTB (0.029).