Microsatellite Instability And Chromosomal Instability In Sporadic Colorectal Cancer

Colorectal cancer is one of the most common tumors in digestive system. It isbelieved that the adenoma-carcinoma sequence underlies the development of colorectalcancer in most patients. There are two genetic instability in colorectal cancer - themicrosatellite instability(MSI) and chromosomal instability (CIN). Discovery of theesetwo pathways has led to the paradigm of colorectal cancer as a geneticallyheterogeneous disease.MSI is a situation in which a microsatellite sequence has gained or lost repeatedunits, often caused by defects in mismatch repair system. MSI present in about 90%HNPCC and 10-15% sprodic colorectal cancer. CIN include allelic losses,choromosomal amplications and translocation. About 60% CRC developed through theCIN pathway. There are difference in clinicopathological characters and geneticbetween tumors with MSI and CIN. But the relationship between them is still unclear.The purpose of this study is to investigate the incidence of microsatellite instability andchromosomal instability in sporadic colorectal carcinoma, and evaluate the relationshipbetween tumor with MSI and CIN. Part One Microsatellite instability in sporad ic colorecta I cancersObjective: To investigate the incidence of microsatellite instability (MSI) insporadic colorectal carcinoma (SCRC) and its association with clinicopathologicalfeatures. Methods: Microsatellite analysis was performed on tissue samples from 112poradic colorectal cancer patients. Microsatellite alterations of BAT225 and BAT26were detected using fluorescent PCR followed by fragment analysis on automatic DNAsequencer with GeneScan 3.1 software. Results: The rate of the high microsatelliteinstability among sporadic colorectal cancer patientswas 12.5 percent, and the rate ofthe microsatellite stability was 78.6 percent. The microsatellite instability phenotypewas correlated with the tumor site and the histopathologic type and the differentiationgrade (P<0.05), while it was independent of the gender, age,tumor invasion, lymphnode metastasis and distance metastasis.Part Two Flow cytometric DNA ploidy in sporadic colorectal carcinomaObjective: To investigate the DNA ploidy in sporadic colorectal carcinoma, andevaluate the relationship between tumor histopathologic parameters ,and MSI status.Methods: Flow cytometry was performed on tissue samples from 40 sporadic colorectalcancer patients (14 MSI-H, 26 MSS) to evaluates the DNA ploidy. Results: 17 and 23cases showed diploidy and aneuploidy respectively.Aneuploidy rate was 57.5 percent.DNA ploidy correlated positively with tumor stage (P<0.05), and the associationbetween aneuploidy and advanced stages of the disease was statistically significant. Nosignificant association was found between DNA ploidy and age,gender, tumor site ,histopathologic type and histologic grade.There was statistically significant correlationbetween the microsatellite instability phenotype and the DNA p loidy (P = 0. 005). Part Three Using comparative genomic hybridization to detectchoromosomal aberration in sporadic colorectal cancerObjective: To investigate the choromosomal aberration in sporadic colorectalcarcinoma, and evaluate the relationship between tumor DNA ploidyand MSI status.Methods: Comparative genomic hybridization (CGH) was used to screen for changes inthe number of DNA sequence copies in 40 sporadic colorectal cancers (14 MSI-H, 26MSS) to identify regions that contain genes important for the development andprogression of colorectal cancer. Results: In 40 sporadic colorectal cancer, we foundfrequent gains at 20q,12q,13q,7p,7q and 16q, while loss was often noted at 18q,5q,4q,8pand 17p。The number of choromosomal aberration is correlated positivelywith tumor stage (P<0.05). No significant association was found between the number ofchoromosomal aberration and tumor site, histopathologic type and histologic grade. Inaneuploidy tumor, there were significantly more gains and losses of choromosomalaberrations than in diploidy tumors. No significant association was found between DNAploidy and choromosomal aberration site. There was statistically significant correlationbetween the microsatellite instability phenotype and the number of choromosomalaberration (P=0.005). In MSS tumor, there were significantly more gains and losses ofchoromosomal aberration than in MSI-H tumors, and the rate of 20q gain and 17p losswere significant higher in MSS tumor than MSI-H tumor.Conclusions1. MSI is a frequent molecular event in sporadic colorectal cancers. Sporadiccolorectal cancers with microsatellite instability may have special clinicopathologicalcharacters.2. DNA ploidy is correlated with tumor stage, aneuploidy are commonly associated with the prognosis of colorectal carcinoma. Sporadic colorectal cancers withmicrosatellite instability were inclined to be diploid.3. Choromosomal aberration exists generally in sporadic colorectal carcinoma, aremore common tha DNA heterploid.4. The number of choromosomal aberration and gain of 20q are correlatedpositively with tumor stage.5. In aneuploidy tumor, there were significantly more gains and losses ofchoromosomal aberrations than in diploidy tumors.6. The regions and frequencies of choromosomal aberration in MSI tumor aresomewhat different from MSS tumors, which may result in the difference ofcarcinogenesis and pathway.