qPCR results revealed that the mRNA quantities of POLH, POLK, POLQ and REV3L in XP-V tumor cells were lower than those of the controls; however, the expression of POLI was higher in the XP-V tumor cells in the absence of UV irradiation (P<0.05; Fig. 5A). The gene discussed is POLK; the disease is xeroderma pigmentosum.