Molecular Epidemiology of Colorectal Cancer

Colorectal cancer (CRC) is one of the most common cancers worldwide and is responsible for 20% of all cancer deaths in developed countries. In Austria, the incidence of CRC is in the top third within the European Union and the second most common cancer-related death in men and women nationwide.
CRC screening policies by endoscopy or stool blood tests are recommended only based on age and family history and yield innumerable individuals with no lesions or lesions with low potential for malignancy. Thus, the discovery of biomarkers that aid in the characterization of risk of progression along the pathway of colorectal carcinogenesis are urgently needed to tailor prevention strategies.

1. Genome-wide association studies (GWAS) of CRC

So far GWAS have identified 40 common low penetrance genetic variants for CRC susceptibility. GWAS have not identified all CRC variants and there is still missing heritability for this disease. Therefore we are under way to conduct CRC GWAS, using 2,700 SNP arrays, based on our large CRC DNA bank comprising more than 13,000 CRC patients, patients with polyps and controls.
The identification of inherited genetic factors involved in CRC susceptibility can help to profile individual risk and may enable early screening and treatment monitoring. CRC genetic susceptibility variants are thus likely to interact with environmental risk factors and they will be incorporated into models of predisposition.

2. Cooperation studies on inherited susceptibility to colorectal cancer COST Action (BM1206)

Colorectal cancer (CRC) is one of the most frequent neoplasms worldwide and an important cause of morbidity in the developed world. It is necessary to identify individuals with a medium to high CRC risk in order to develop adequate preventive measures.
The main objective of this action is to comprehensively understand the impact of inherited susceptibility in CRC for profiling individual disease risk and performing early screening and treatment monitoring. By doing so, new molecular biomarkers will be implemented and validated for personalized CRC medicine.
The following specific objectives will be pursued in order to achieve the previous general aim:

2.1. Identification of new CRC susceptibility variants:
A polygenic model of inherited susceptibility to CRC implies the co-inheritance of multiple risk variants. So far, 30 common, low-penetrance genetic variants for CRC susceptibility have been identified by GWAS. This Action will permit to boost sample size and statistical power (participating cohorts sum up more than 50,000 cases and 50,000 controls) and, therefore, it is very likely that additional genetic variants linked to CRC will be identified. Large-scale meta-analyses of existing and newly generated GWAS data will be performed and replication of initial GWAS findings in additional cohorts will be used to robustly confirm those genetic variants that participate in CRC susceptibility.

2.2. Functional links for CRC susceptibility variants:
Most GWAS variants are unlikely to alter protein function and fine mapping and functional studies will be used to identify a correlated functional variant. The identification of the functional variation that causes increased CRC risk may lead to the development of new means of preventing the disease. However, the journey from the associated polymorphism to functional variant is not simple and will require additional work. In order to perform an initial search for readily identifiable functional variants, fine mapping in the regions close to each disease-associated single nucleotide polymorphism (SNP) or copy number variant (CNV) should be undertaken, enriching for variants in strong linkage disequilibrium (LD) with that SNP and with possible functional effects. Basic functional work should also be performed, such as assessing the levels of mRNAs and proteins in each region in patients of known genotypes, as well as more complex studies such as chromatin mapping, gene reporter and allele-specific expression experiments.

2.3. Genetic variants involved in CRC survival and treatment toxicity:
CRC genetic susceptibility variants could also act as biomarkers for CRC survival and treatment response. For instance, inherited genetic variants can modulate the pharmacokinetics/pharmacodynamics of drugs used in CRC treatment by substantially affecting individual response and toxicity to chemotherapy. Therefore, GWAS data will be analyzed regarding CRC survival and treatment toxicity in order to identify genetic variants linked to differential prognosis and adverse drug reactions.

2.4. Genetic variants enriched in CRC subgroups:
The impact of CRC susceptibility genetic variation will not be universally generic and some of the risk variants will impact preferentially on CRC subtypes, such as early-onset or microsatellite-unstable CRC (MSI+ CRC). If some of the CRC genetic susceptibility variants appear to be associated with some clinical and familial features, it could have potential important implications for screening and surveillance strategies for this disease.

2.5. New predisposition genes for CRC in families with unknown genetic basis:
Next generation sequencing will be useful to identify new CRC predisposition genes in selected high-risk and early-onset families with unknown genetic basis from the participating cohorts.

2.6. Interactions between CRC susceptibility variants and environment:
CRC risk is undoubtedly determined by complex interactions between genetic and lifestyle/dietary risk factors. Epidemiological studies have established several dietary risk factors for colorectal neoplasia; these include low vegetable and high red meat consumption and micronutrient deficiency and excessive alcohol intake. CRC genetic susceptibility variants are thus likely to interact with these environmental lifestyle risk factors to modify risk and they should be incorporated into models of predisposition.

2.7. High-risk CRC profile of inherited variants by statistical modeling:
Besides gene-environment interactions, it is also entirely conceivable that epistatic interactions between CRC genetic susceptibility variants may exist. A high-risk CRC profile using mentioned parameters could be developed using data from all participating cohorts and be very useful as a molecular tool for personalized CRC medicine.

3. Metabolomic profiles throughout the continuum of colorectal carcinogenesis (TRANSCAN)

Metabolomics is an innovative and powerful approach by which a large number of metabolites are systematically screened to characterize biological phenotypes with an unprecedented level of precision. New biomarkers that help characterize risk of progression along the pathway of colorectal carcinogenesis are urgently needed to tailor prevention strategies.
By investigating plasma from individuals free of colorectal tumors, patients with colorectal adenoma, and patients with colorectal cancer (CRC, stage I-IV), the newly formed MetaboCCC Consortium aims to investigate changes in the metabolome along the continuum of colorectal carcinogenesis. We will perform metabolomic analyses in 2,300 plasma samples derived from well-defined populations of four TRANSCAN countries (the Netherlands, Germany, Austria, Norway) with assays completed at an expert site (France), using multiple discovery and replication sets to define biologic mechanisms of colorectal carcinogenesis. For a comprehensive and complementary strategy, we will apply both targeted and untargeted metabolomics.
We aim to a) determine preventive or predisposing plasma metabolites discerning adenoma cases from controls, b) determine plasma metabolites that characterize CRC, compared with controls or adenoma cases, and c) test for markers that discern CRC stages.
We expect that the discovery of novel metabolites in blood that define the transition between various stages of colorectal carcinogenesis can be used in the future for risk stratification, including for tailored prevention strategies by endoscopy.

4. Biomarkers related to folate-dependent one-carbon metabolism in colorectal cancer recurrence and survival (TRANSCAN)

Colorectal cancer (CRC) is the second leading cause of cancer death. At the same time, the number of survivors of CRC continues to increase. Many cancer patients resort to taking nutritional supplements, assuming potential benefits. However, in the case of folate this assumption may be wrong, since high folate may stimulate the growth of established cancer. Folate is involved in one-carbon metabolism, impacts DNA synthesis, and supports tumor growth. Within a large consortium of parallel European CRC patient cohorts we will be able to investigate, comprehensively, the role of folate from diet and supplements, the impact on a state-of-the art set of one-carbon metabolism biomarkers, and their joint influence on clinical outcomes, including recurrence, survival and treatment toxicity. Our study aims to investigate whether prognosis in stage I-III CRC is related to folate status at different time-intervals in 1584 CRC patients. Both key biomarkers of folate-mediated one-carbon metabolism (FOCM) and diet/supplements will be investigated as components of folate status prior to surgery, and at 6 and 12 months past surgery. Further, we propose to determine whether biomarkers related to FOCM are associated with folate intake, and explore whether folate status modifies treatment toxicity in patients who underwent 5-FU chemotherapy.
We leverage unique resources and expect that by unraveling the effect of the folate and FOCM biomarkers on CRC prognosis we will be able to provide clinically relevant advice to cancer patients and define future tertiary prevention strategies.