Background: We previously reported that genetic variant in the CCL5/CCR5 pathway predict efficacy of regorafenib in metastatic colorectal cancer patients (mCRC). CCL5 rs2280789 G allele and CCL5 rs3817655 T allele were associated with longer overall survival (OS) and severe skin toxicity due to low VEGF-A production via endothelial progenitor cell (EPC). CCL4 rs1634517 G allele and CCL3 rs1130371 C allele correlated with longer Progression-free survival (PFS) and OS. We investigated the biological role of CCL4 and CCL3 gene polymorphisms. Methods: We analyzed genomic DNA extracted from 79 samples of a Japanese cohort receiving regorafenib. Single nucleotide polymorphisms (SNPs) of genes in CCL5/CCR5 pathway were analyzed by PCR-based direct sequencing. Blood samples were obtained from 57 patients at baseline (BL), day 21 and progressive disease (PD), and serum CCR5, CCR5 ligands (CCL3, CCL4, CCL5) and VEGF-A levels were measured using ELISA. PFS and OS were analyzed using Kaplan-Meier curves and log-rank test. Results: Increased CCL3 levels at PD were associated with longer OS than decreased (12.6 vs 4.8 mos, P = 0.003). Patients with decreased CCL4 levels at day 21 had a trend toward longer PFS and tumor shrinkage. Positive correlation was observed between CCL3 and CCR5 throughout the treatment independent of other ligands (change at day 21: r = 0.426, P = 0.009). There was no significant correlation of CCL3 and CCL4 levels with VEGF-A levels. Patients with the G/G variant in CCL3 rs1130371 had increased CCL3, CCR5 and CCL5 levels at day 21 than any A allele. Similarly, patients with the C/C variant had increased CCL3, CCR5 and CCL5 levels at day 21 compared with those with any A allele. In contrast, both CCL5 rs2280789 G allele and CCL5 rs3817655 T allele were associated with increased CCL3 levels and decreased CCL4 levels at day 21 (P = 0.006, P = 0.043; P = 0.006, P = 0.043). Conclusions: Positive correlation of CCL3, CCR5 and CCL5 impact similarly on CCL3 and CCL4 SNPs, while different manner between CCL3 and CCL4 was found in CCL5 SNPs. This suggests an alternative mechanism of action in the network of CCR5 and the ligands except CCL5-VEGF-A signaling via EPC in mCRC patients receiving regorafenib.