HPRT1 and gastric cancer: In this study, we investigated the five reference genes that have been most frequently used genes in stomach cancer studies (ACTB, GAPDH, B2M, 18S rRNA, and HPRT1) and for comparison, RPL29, a reference gene used in other cancer studies, in 'non-stomach cancer cell lines', 'stomach cancer cell lines', 'normal stomach tissues' and 'tumor stomach tissues' (Table 1).