**5. Conclusion**

In general, the studies suggest that the *XPD* Lys751Gln and *XPD* Asp312Asn polymorphisms may be associated with risk of colorectal adenomas with the possibility of interaction with smoking and alcohol consumption. The reported studies of polymorphisms in *XPC* and *XPA* in relation to risk of colorectal cancer are few, but the results are relatively consistent: In general, no association of the polymorphisms in the genes involved in NER (*XPD*, *XPC*, *XPA* and *ERCC1*) was observed with risk of colorectal cancer. A possible interpretation of the results may be that the polymorphisms in the genes *XPD*, *XPC*, *XPA*  and *ERCC1* are not of major importance in colorectal cancer carcinogenesis, which points towards that lowered repair capacity of the NER pathway may not be a risk factor for development of colorectal cancer.

The results were generally inconsistent or too few to compare to highlight any trend and no strong associations were observed for risk of colorectal adenomas or colorectal cancer. Overall, the role of genetic variants as SNPs in genes involved in NER is not satisfactorily clarified at present. It is possible that some of the SNPs may contribute to development of adenomas or colorectal cancer only in concomitance with certain dietary and life style factors. Furthermore, it may be only the joint effect of multiple polymorphisms that will provide us with information about genetic susceptibility for colorectal cancer. Larger carefully designed studies with stratified/adjusted analyses of gene-gene and geneenvironment interactions may be required in the future to achieve convincing statistically significant results on factors involved in colorectal carcinogenesis.
