WHAT IS KNOWN AND OBJECTIVE: High interindividual response variability was 
reported with capecitabine and oxaliplatin (CAPOX) regimen in colorectal cancer 
(CRC). The single nucleotide polymorphisms (SNPs) of the genes related to drug 
efflux transport (ABCB1) and DNA repair (ERCC) could result in altered tumour 
response. Hence, this study was designed to assess the influence of ABCB1, 
ERCC-1 and ERCC-2 gene polymorphisms on tumour response to CAPOX treatment in 
CRC patients of South Indian origin.
PATIENTS AND METHODS: A total of 145 newly diagnosed CRC patients were included 
in the final analysis. Response to CAPOX treatment in the adjuvant setting was 
assessed in terms of disease-free survival rate (DFSR) and overall survival rate 
(OSR) at 3 years, whereas in the palliative setting, the response was assessed 
as progression-free survival rate (PFSR) and OSR at 3 years. Five millilitres of 
the venous blood sample was collected from each patient for genomic DNA 
extraction by the manual phenol-chloroform method. Genotyping and allelic 
discrimination analysis were done using real-time PCR (RT-PCR).
RESULTS AND DISCUSSION: With ABCB1 gene polymorphism rs1045642 (A > G), patients 
with AG/GG genotype showed better DFSR [P value = .02, OR = 2 (CI: 1.5-3)] and 
PFSR [P value = .02, OR = 1.6 (CI: 1.1-2.5)] when compared to AA genotype in the 
adjuvant and palliative settings, respectively. Similarly with rs1128503 (A > G) 
polymorphism, patients with AG/GG genotype were found to have better DFSR [P 
value = .02, OR = 1.9 (CI: 1.3-3)] and PFSR [P value = .01, OR = 2 (CI: 
1.1-3.7)] when compared to AA genotype. However, we did not find any association 
between CAPOX response and ABCB1 gene polymorphisms in a binary logistic 
regression when non-genetic predictors were considered for analysis. We did not 
find any association with ERCC1 (rs11615 A > G) and ERCC2 (rs13181 T > G) gene 
polymorphisms with respect to CAPOX response in either of the treatment 
settings.
WHAT IS NEW AND CONCLUSION: The response to CAPOX treatment was found to be 
influenced by the ABCB1 gene variants (rs1128503 and rs1045642), thereby 
strengthening their predictive role. No association was found between ERCC1 
(rs11615 A > G), ERCC2 (rs13181 T > G) gene polymorphisms and tumour response to 
CAPOX treatment in CRC patients of South Indian origin.