11. Early Detection of CRC
Unfortunately, the majority of CRC is not detected early. About 50% of the CRC patients are diagnosed at advanced tumor stages presenting poor prognosis [2]. Therefore, early screening for CRC has become one of the greatest public health challenges over the last fifty years. Development of genomic signatures that can be used for diagnosis and prognosis will be of interest, because many screening tests are invasive and/or expensive [38]. Currently established screening tests are fecal occult blood testing (FOBT) and colonoscopy. However, the sensitivity for detecting adenomas with FOBT is very low [39]. Moreover, the compliance for colonoscopy is quite low because it is time consuming, disturbing, painful and involving some risk [40]. A CRC screening test that accurately detects advanced adenomas with a high potential of malignant progression would be desirable [41]. Consequently, innovative screening tools are necessary for the detection of a pre-cancer condition and very early-stage malignancies in a healthy population allowing curative treatment interventions. A first excellent example may become the recently developed non-invasive multitarget stool DNA test (Cologuard™) for colorectal cancer screening that includes besides KRAS mutation analysis, detection of the methylation status of the NDRG4 and BMP3 genes. Indeed, this novel test was able to detect advanced precancerous lesions with much higher sensitivity than fecal immunochemical test (FIT) (42.4% vs. 23.8%, p < 0.001) [42]. The blood-based Septin 9 DNA methylation assay (Epi proColon) represents another example which has shown that DNA methylation markers can be of great importance for early detection of CRC. Using highly sensitive real-time PCR aberrantly methylated tumor-derived DNA of the Septin 9 gene can be detected in blood plasma [43]. One recent approach for serum based detection of CRC uses biochip array technology [2] applying competitive and sandwich assay techniques using antibodies as capture molecules [44]. For this purpose, a multiplex serum protein biochip array was developed for the determination of nine serum markers. Significant differences between cases and controls were observed in serum levels of these markers [2]. It was the first study reporting the development of a multiplex protein array for clinical application to CRC screening. Advantage of this array is that the required sample volume is very low and the throughput is high: 1200 samples can be simultaneously analyzed for the nine serum markers in one hour using a fully automated biochip immunoassay analyzer. [44]. A combination of FOBT and the biochip array may improve the performance of CRC screening because neither compliance nor diagnostic performance of both methods alone seems to be satisfying. Another approach for developing blood serum based diagnostic screening test for early detection of CRC used the expression of miRNAs. Using a global microarray, characteristic changes in the expression level of miRNA molecules in plasma were discovered between CRC patients and healthy controls [45]. Additionally, miRNA expression alterations were also observed within stool samples by use of microarray expression studies [41]. Both plasma and stool samples seem well-suited for screening processes [41]. Analysis of miRNA molecules has opened new opportunities for a quantitative and non-invasive diagnostic approach for CRC screening in the future. Research groups are standardizing test conditions in a prospective validation study. The goal is to develop a chip-based diagnostic test that facilitates molecular screening for CRC [41]. Moreover, the GenomeLab Genetic Analysis System presents a novel technology platform for custom design of multiplexed gene expression analysis (GeXP assay). Only nanograms of total RNA are necessary to allow exact quantification of multiple targets simultaneously in a single reaction [46].