Systematic Review of Candidate Single-nucleotide Polymorphisms as Biomarkers for Responsiveness to Neoadjuvant Chemoradiation for Rectal Cancer.

BACKGROUND/AIM: Treatment of rectal cancer has improved significantly with the addition of neoadjuvant chemoradiation. Certain patients have experienced a complete pathological response to chemoradiation, as observed in surgically resected tissue samples, thus calling into question the necessity of radical surgery in this population of patients. Pharmacogenetic studies now implicate the role that genetic biomarkers, such as single nucleotide polymorphisms, play in an individual's response to chemoradiation. The aim of this review was to provide a comprehensive evaluation of a group of candidate single nucleotide polymorphisms associated with chemoradiotherapy response and an assessment of techniques that can be used to easily identify the presence of these single nucleotide polymorphisms in patient samples. MATERIALS AND METHODS: Relevant primary research articles were identified in the Medline Database from January 1, 2006 to May 31, 2012. We included nine relevant articles addressing the correlation between six candidate single nucleotide polymorphisms and one candidate variable number tandem repeat in six genes, namely thymidylate synthase, epidermal growth factor, epidermal growth factor receptor, superoxide dismutase 2, interleukin-13, and cyclin D1, with tumor down-staging and patient survival after neoadjuvant chemotherapy or chemoradiotherapy. RESULTS: Specific alleles of each of the candidate single nucleotide polymorphisms were significantly associated with either a major response in tumor down-staging or a minor to non-existent response following neoadjuvant chemotherapy, individually or in combination with other single nucleotide polymorphisms. However, studies present conflicting results regarding the effect of certain candidate single nucleotide polymorphisms on tumor down-staging. CONCLUSION: Through further research into candidate single nucleotide polymorphisms and potential identification of other polymorphisms, clinicians may be able to create individualized treatment plans in accordance with the genotype of individual patients with rectal cancer, in order to reduce morbidity and mortality.

A common variant in MTHFR influences response to chemoradiotherapy and recurrence of rectal cancer.

An important determinant of the pathogenesis and prognosis of various diseases is inherited genetic variation. Single-nucleotide polymorphisms (SNPs), variations at a single base position, have been identified in both protein-coding and noncoding DNA sequences, but the vast majority of millions of those variants are far from being functionally understood. Here we show that a common variant in the gene MTHFR [rs1801133 (C>T)] not only influences response to neoadjuvant chemoradiotherapy in patients with rectal cancer, but it also influences recurrence of the disease itself. More specifically, patients with the homozygous ancestral (wild type) genotype (C/C) were 2.91 times more likely (291% increased benefit) to respond to neoadjuvant chemoradiotherapy {95% CI: [1.23, 6.89]; P=0.0150} and 3.25 times more likely (325% increased benefit) not to experience recurrence of the disease {95% CI: [1.37, 7.72]; P=0.0079} than patients with either the heterozygous (C/T) or the homozygous mutation (T/T) genotype. These results identify MTHFR as an important genetic marker and open up new, pharmacogenomic strategies in the treatment and management of rectal cancer.