PPIA and neoplasm: We identified reliable genes for individual expression profiling of the cell lines, the normalization of A431 may be done by PGK1, RPL37A and PSMC4; A549 by RPLPO, UBC, GAPDH, MT-ATP6, CASC3 and PES1; and BxPC3 by RPL37A, RPLPO and CASC3. However, the 5 ECGs-- TBP, UBC, RPLPO, PPIA, PSMC4-- can be taken as the most suitable candidate reference genes for radiation response expression profiling in the tumor models studied.