GAPDH and cancer: We investigated the experimental conditions commonly used to study radiotherapy-induced changes in the expression of CRC-associated genes and estimated the expression stabilities of 14 HKGs commonly used as RGs in CRC radiotherapy studies, including GAPDH and ACTB. These genes are encoded by RNA polymerase II and represent diverse basic cellular pathways in normal cells, therefore, reducing the possibility of co-regulated genes that may induce potential artifacts in estimating the response to radiation therapy in heterogeneous cancer cells.