ABSTRACT
BACKGROUND AND AIM: Longstanding ulcerative colitis (UC) predisposes to colorectal cancer (CRC). To understand the molecular pathogenesis of colitis-associated colorectal neoplasia (UC-CRN), we studied the frequency of microsatellite instability (MSI) and mutations in p53, BRAF and KRAS genes in the tissues of patients with long standing UC with or without neoplasia and compared them with colitis patients without risk of neoplasia, and those with sporadic colorectal neoplasia (S-CRN) in an area with lower prevalence for either disease. METHODS: Biopsies were obtained during magnifying chromo colonoscopy or routine colonoscopy in consecutive UC patients with high risk (UC-HR) and low risk (UC-LR) of neoplasia, and those with S-CRN. MSI (NCI-Bethesda panel) and mutations in p53, KRAS and BRAF genes were analysed. RESULTS: Twenty-eight patients with UC-HR, 30 with UC-LR and 30 with S-CRN were included. Six (21.4%) of UC-HR had neoplasia (Progressors). MSI was not detected in the UC-CRN group as compared to 5 (16.7%) in the S-CRN group. p53 mutations occurred in 1 (3.3%) of UC-LR, increasing to 6 (27.3%, P<0.05) and 3 (50%, P<0.05) in the UC-HR subgroups without and with neoplasia respectively, as against 10 (33.3%) in sporadic neoplasia group. KRAS mutations were found only in the presence of neoplasia. None showed the BRAF mutation. CONCLUSIONS: In a population with a lower prevalence for UC and CRC, the molecular pathogenesis of colitis-associated colorectal neoplasia is comparable to that reported from areas with a higher prevalence of these diseases, MSI being an exception.
Subject(s)
Adenocarcinoma/genetics , Adenoma/genetics , Biomarkers, Tumor/genetics , Colitis, Ulcerative/genetics , Colonoscopy , Colorectal Neoplasms/genetics , Adenocarcinoma/epidemiology , Adenocarcinoma/etiology , Adenocarcinoma/pathology , Adenoma/epidemiology , Adenoma/etiology , Adenoma/pathology , Adult , Colitis, Ulcerative/complications , Colitis, Ulcerative/epidemiology , Colitis, Ulcerative/pathology , Colonoscopy/methods , Colorectal Neoplasms/epidemiology , Colorectal Neoplasms/etiology , Colorectal Neoplasms/pathology , DNA Mutational Analysis , Disease Progression , Female , Genes, p53 , Genetic Markers , Humans , India/epidemiology , Male , Microsatellite Instability , Middle Aged , Polymerase Chain Reaction , Prevalence , Proto-Oncogene Proteins/genetics , Proto-Oncogene Proteins B-raf/genetics , Proto-Oncogene Proteins p21(ras) , Risk , ras Proteins/geneticsABSTRACT
Evaluation of genetic alterations in inhabitants of an area of Tamil Nadu, India, chronically exposed to high background radiation (HBRA), was the major purpose of the present study. A total of 216 samples (exposed inhabitants, 108; control subjects, 108) were selected based on the confirmation of radiation dose level using thermoluminescence dosimetry (TLD). After signing a consent form, volunteers provided blood samples (5 ml each) to establish cell cultures at 52 h. One hundred complete metaphase cells from each subject were evaluated for karyotyping. The frequencies of chromosomal alterations (CA) were found to be higher in the exposed groups and the aberrations predominately observed were of chromatid-type. Smoking was found to have considerable effect on the frequency of CA in exposed subjects. With the comet assay for DNA damage, a significant increase in comet tail frequency was also observed in exposed subjects compared to controls. At present there are no radioepidemiological data regarding the cytogenetic studies in these areas. Furthermore, the Kudankulam nuclear power plant nuclear power plant is being constructed in the same area. The study gives potentially important information on the general health effects due to radiation exposure and increases people's understanding of the hazardous nature of chronic low level natural radiation exposure. However, we may conclude that the HBRA by itself does not pose any significant risk of genetic damage as measured by conventional cytogenetic analysis.