When comparing the frequency of GSTM1 null allele in CRC cases between our study and the study by Hlavata et al. [11], significant differences were observed for the GSTM1 null allele (53.9% vs. 50.8%), while frequency of GSTT1 null allele was almost identical between our study and their study (20.8% vs. 20.3%). Here, GSTM1 is linked to colorectal carcinoma.