Analyzing the association of cancer risk with diplotypes (Table 3) it was observed that the presence of SHMT1 T allele decreased the risk of rectal cancer only in case of wild type MTHFR. As had been expected from the results of genotype analysis the risk reducing effect of SHMT1 T allele was completely abolished when the MTHFR T allele was present. This evidence concerns the gene SHMT1 and rectal cancer.