Correlation of genetic and epigenetic alterations with treatment outcome of concurrent chemoradiation treatment (CRT) in cervical cancer-medical conference in bangalore
The 2015 estimates of cervical cancer account for a total of 527,624 new cervical cancer cases and 265,672 deaths all around the world. Cervical cancer estimates among Indian women aged between 15 to 44 years was reported as 122,844 new cases of which 67,477 resulted in death. Polymorphic gene variants, mRNA expression and epigenetic alterations of genes may alter DNA repair capacity and influence cancer progression and clinical responses to chemoradiotherapy.
Objective: To investigate single nucleotide polymorphisms (SNPs) in human cytokine and DNA repair genes along with promoter methylation as well as expression of MGMT gene and their correlation with treatment outcome/overall survival after concurrent chemoradiation treatment (CRT) in north Indian cervical cancer patients.
Methodology: All clinical details of cervical cancer patients and age-matched healthy controls were taken after informed consent and ethical approval. Blood samples in EDTA were taken for DNA and RNA isolation and SNPs were genotyped by PCR-RFLP and ARMS-PCR. Promoter methylation of MGMT gene was done by EpiTect® Bisulfite QIAGEN® Kit and expression was quantified by real-time PCR using SYBR Green assay. All data were analyzed by using Fisher’s exact probability test and χ2 test. Out of the total cervical cancer cases (n=246), 48 cases were followed for 36 months (2013-2016) to see the effect of cisplatin based concurrent chemoradiation (CRT).
Results: SNPs in cytokine genes (IL-1RN, IL-6 and TNF-a ) and DNA repair genes (XRCC4, OGG1 and MGMT) showed highly significant association. The gene variants, IL-1β -597T/C and MGMT Lys178Arg A/G showed significant association with vital status of cervical cancer (P< 0.005). The methylation status of MGMT gene showed significant association with overall survival (P=0.001). The mean age of cervical cancer cases who received CRT was 48.44±11.45 years. Response of cases was observed after the completion of treatment. The median overall survival of methylated cases was 17 months and unmethylated was 25 months. The Log-rank test showed unmethylated cases with significantly higher survival rates as compared to cases with MGMT methylation (17 vs 25, P=0.0001; HR (95%CI)=8.071 (3.959-16.46). It was observed by stage-stratified analysis that the overall survival among patients with stage II was better than stage III/IV (29.0 vs 20.0, P=0.0022; HR (95% CI)=0.351 (0.169-0.726). It was clear that cases with higher expression levels of MGMT gene showed higher survival (27.0 months) as compared to those with lower expression (21.0 months), however the difference was not significant [P=0.142; HR (95%CI)= 0.570 (0.270-1.203)].
Conclusion: Identification of disease phenotype by the modifying effects of polymorphic variants of cytokine and DNA repair genes in cervical cancer will have clinical importance leading to the discovery of newer factors possibly contributing to the development of disease.