HPRT1 and gastric cancer: In an evaluation of 115 articles published from May 2007 to November 2009, we found that GAPDH (53 cases; 46.1%) and ACTB (41 cases; 35.7%) were the most frequently used reference genes in gastric cancer studies; followed by 18S rRNA (8 cases; 7.0%), beta-2-microglobulin (B2M; 3 cases; 2.6%), hypoxanthine phosphoribosyl transferase 1 (HPRT1; 2cases; 1.7%), TATA binding protein (TBP; 1 case; 0.9%), and beta-tubulin (TUBB; 1 case; 0.9%).