Tumor response is predicted by patient genetic profile in rectal cancer patients treated with neo-adjuvant chemo-radiotherapy

The aim of the study was the identification of a pharmacogenetic profile predictive of the tumor regression grade (TRG), considered as tumor response parameter, after neo-adjuvant treatment in rectal cancer patients. A total of 238 rectal cancer patients treated in a neo-adjuvant setting by a fluoropyrimidines-based chemo-radiotherapy (RT) were genotyped for 25 genetic polymorphisms in 16 genes relevant for treatment-associated pathways. Two polymorphisms were associated with TRG in a multivariate analysis: hOGG1 -1245C>G, which can affect radiosensitivity and MTHFR -677C>T, which is involved in fluoropyrimidines action. Patients bearing at least one variant allele had a lower chance to get TRG⩽2 (OR=0.46 95% CI 0.23–0.90, P =0.024; and OR=0.48 95% CI 0.24–0.96, P =0.034; respectively). An association trend was observed for ABCB1 -3435C>T, which is responsible for the multi-drug resistance (odds ratio (OR)=1.96, 95% confidence interval (CI) 0.98–3.95, P =0.057). Exploratory classification and regression tree (CART) analysis highlighted high-order gene–gene and gene–environment interactions and a genetic signature associated with differential response, with hOGG1 -1245C>G as the most predictive factor. Other significant variables were: ABCB1 -3435C>T, MTHFR -677C>T, ERCC1 -8092C>A, ABCC2 -1249G>A, XRCC1 -28152G>A, XRCC3 -4541A>G and patients gender. On the basis of CART results, patients were categorized into three groups according to tumor response probability: intermediate and high profiles had a higher probability to get TRG⩽2 as compared with low profiles (OR=4.12 95% CI 1.46–11.65, P T polymorphisms in the tumor response of rectal cancer patients treated with chemo-RT in neo-adjuvant setting, and shows the relevance of gene–gene and gene–environment interactions for complex phenotypes as tumor response.