Cancer stem cell gene variants and colon cancer outcome

In the absence of adjuvant chemotherapy, approximately 50% of colon cancer patients with resectable disease are cured by surgery alone, whereas 50% relapse. Using adjuvant chemotherapy following surgery rescues approximately 15% of patients from the relapsing group. In current practice, the majority of these colon cancer patients receive adjuvant treatment unnecessarily, either because they were cured by surgery alone or because they will relapse despite adjuvant treatment. It is therefore essential to identify patients who will benefit from adjuvant therapy, sparing others needless toxicity and the financial burden of chemotherapy that will not work. Thus, there is intense interest in the elucidation of prognostic and predictive biomarkers in colon cancer that will improve outcome through patient classification. Growing evidence suggests that human cancers are stem cell diseases and only a small subpopulation of cancer cells, endowed with stem cell-like features, might be responsible for tumor initiation, progression and chemoresistance. There is substantial germline genetic variability within the genes used as markers to identify colon cancer stem cells, including multiple single nucleotide polymorphisms. These common DNA-sequence variations may result in altered gene function and/or activity thereby causing inter-individual differences in patient`s tumor recurrence capacity and chemoresistance. In a recent study, we investigated 25 germline polymorphisms in a comprehensive panel of genes that have been previously associated with colon cancer stem cells to predict tumor recurrence in 234 patients with stage III and high-risk stage II colon cancer treated with 5-FU based chemotherapy and found that time to tumor recurrence varies according to CD44, ALCAM, LGR5 and ALDH1A1 genotypes, thus representing valuable and promising genetic biomarkers. In the proposed project we will investigate the genetic biomarkers based on our preliminary findings in a large and independent study cohort of 1061 stage II and III colon cancer patients to validate the single biomarkers CD44 rs8193 C>T, ALCAM rs1157 G>A and LGR5 rs17109924 T>C and our predictive model (gene variant profile) including CD44 rs8193 C>T, ALCAM rs1157 G>A, LGR5 rs17109924 T>C and ALDH1A1 rs1342024 G>C in colon cancer patients treated with 5-FU based chemotherapy and to evaluate the single genetic biomarkers and our gene variant profile in colon cancer patients treated with surgery alone to clarify their prognostic and/or predictive role. Our findings may result in a decreased incidence of tumor relapse in stage II and III colon cancer by placing patients on adjuvant therapy that would not have been initiated in current circumstances. Conversely, our results may allow avoiding treating patients at low risk, thus eliminating the morbidity associated with adjuvant therapies. Overall, this study will generate new scientific knowledge and insights into adjuvant colon cancer to improve clinical practice and individualized patient treatment.

We recently investigated 25 gene variants in a comprehensive panel of genes that have been previously associated with colon cancer stem cells to predict tumour recurrence in patients with stage III and high-risk stage II colon cancer treated with 5-FU based chemotherapy. We found the minor alleles of CD44 rs8193 C>T, ALCAM rs1157 G>A and LGR5 rs17109924 T>C significantly associated with increased time to recurrence (TTR). In this study we validated these genetic biomarkers in a large and independent study cohort to clarify their predictive and/ or prognostic role. A total of 742 consecutively collected patients with stage II and III colon cancer were included in this validation study. Genomic DNA was analysed for CD44 rs8193, ALCAM rs1157 and LGR5 rs17109924 gene variants. The tested gene variants CD44 rs8193 and ALCAM rs1157 did not show a statistically significant association with TTR in the analyses. However, patients carrying at least one C allele in LGR5 rs17109924 had a significantly increased TTR compared to patients carrying the homozygous T/T variant. Stratified by adjuvant chemotherapy, LGR5 rs17109924 was highly significant for patients receiving adjuvant chemotherapy whereas no association was found for patients without adjuvant chemotherapy. Also after adjusting for sex, age, clinical stage, number of resected lymph nodes, lymphovascular, vascular and perineural invasion in multivariate analysis, LGR5 rs17109924 remained statistically significant for patients with adjuvant chemotherapy. We confirmed in a large and independent study cohort that LGR5 rs17109924 is a predictive genetic biomarker for 5-FU based adjuvant chemotherapy in patients with colon cancer. Our results provide a strategy for stratifying patients for benefit of adjuvant chemotherapy, which in turn would allow treatment options to be tailored to the individual.