In conclusion, the results obtained in this systematic review suggest that according to the recent literature, as well as the four SNPs of current clinical relevance in DPYD, there are other SNPs in genes related to the PD (TYMS, ENOSF1, MTHFR, ERCC1, and ERCC2) and PK (CDA, DPYD, UMPS, and SLC22A7) of capecitabine that could come to be considered in the future as predictive biomarkers of the outcomes of capecitabine-based therapy in patients with CRC. The gene discussed is CDA; the disease is colorectal carcinoma.