Correlation of the C>T SNP (rs16906252) with MGMT Promoter Hypermethylation, KRAS Mutation Status and Clinicopathologic Features in Colorectal Cancer
Catherine E Hagen, Joel A Lefferts, Gregory J Tsongalis, Laura J Tafe. Dartmouth-Hitchcock Medical Center, Lebanon, NH
Background: Promoter hypermethylation of O6-methylguanine-DNA methyltransferase (MGMT), a DNA repair enzyme, is an early event in the carcinogenesis of colorectal cancer (CRC). Recent data show an association between MGMT methylation and the C>T SNP (rs16906252) within the first exon of MGMT. The goal of our study was to determine the prevalence of the C>T SNP (rs16906252) in a group of patients with CRC and to associate these findings with MGMT methylation status, KRAS mutation status, pathologic features, and patient mortality data.
Design: Thirty-five patients (mean age 61.7; M:F 18:17; average follow up 43 mos.) with a history of CRC were included. DNA previously extracted from formalin-fixed, paraffin-embedded tumor tissue for determination of KRAS status was used for analysis. MGMT methylation status was determined using bisulfite converted DNA. DNA concentrations ranged from 0.9 ng/uL to 910 ng/ul as determined by UV spectrophotometry. DNA (10 ng/uL) was amplified using primers flanking the C>T SNP and genotyping was performed using TaqMan probes specific for the C and T alleles. Pathologic and clinical information were collected through medical chart review.
Results: Two patients (5.7%) were found to be heterozygous for the C>T SNP. No patients were found to be homozygous for the T allele. In our cohort the frequency of the T allele was 4%. Ten patients (32.3%) were positive for MGMT methylation. Of the two C>T SNP heterozygous patients, one was associated with MGMT methylation (10% of methylated group) while the other was unmethylated (4% of unmethylated group). Neither of the SNP heterozygous patients had an associated KRAS mutation. The average age of the heterozygous SNP patients was 68.5 yrs. compared to 60.9 yrs. in the wild type group. Both heterozygotes were male with left-sided CRC. One was pathologic stage 3 at diagnosis while the other was stage 4. One was deceased at last follow-up while the other was still living (average follow-up 41 mos.).
Conclusions: Although our rate of MGMT methylation in CRC (32.3%) is similar to previously reported values, in our population, the overall rate of C>T SNP (rs16906252) is much lower than previously reported. There was no association with the C>T SNP and KRAS status. Further studies are needed to understand the relationship of MGMT methylation in CRC and the C>T SNP (rs16906252) in given populations.
Monday, March 4, 2013 1:00 PM
Poster Session II # 130, Monday Afternoon