PPIC and neoplasm: Although background expression of EMP2, PPIC, DKFZp762E1312, and SLC6A8 was detected in the unspiked blood, increasing expression levels of the respective genes were observed when tumor cells had been added to the blood, with a detection limit of 3 (EMP2, PPIC) and 26 tumor cells per ml of blood (DKFZp762E1312, SLC6A8).