HPRT1 and colorectal neoplasm: The genes evaluated in their study included hypoxanthine-guanine phosphoribosyltransferase 1 (HPRT), beta-actin (ACTB), mitochondrial ribosomal protein L19 (MRPL19), beta-2-microglobulin (B2M), GAPDH, and PPIA (peptidyl-prolyl isomerize A), where they reported B2M and PPIA as the most stably expressed genes on colorectal tumor [24].