Analysis Of The Intratumoral Heterogeneity Of Gene Methylation And Its Clinical Significance In Papillary Thyroid Carcinoma

Background and Objective:Thyroid cancer is the most common malignant tumor in endocrine system,and its incidence has been increasing rapidly in recent years.Papillary thyroid carcinoma is the most common histological type of thyroid cancer.The majority of papillary thyroid carcinomas are inert,but there are still a small number of patients can appear extrathyroidal invasion,lymph node metastasis as well as distant metastasis.Lack of effective diagnostic methods for aggressive papillary thyroid carcinoma is the key limiting therapeutic efficacy or leading to overtreatment,and it is also an important scientific problem to be solved.Tumor heterogeneity is one of the characteristics of malignant tumors,which is related to tumor aggressive behavior and drug resistance.According to previous reports,papillary thyroid carcinoma has less mutation load than epigenetic changes.And epigenetic changes can affect gene function so as to influence biological behavior.This study aims to explore the intratumoral heterogeneity of papillary thyroid carcinoma from the perspective of DNA methylation,and explore the diagnostic value of intratumoral methylation heterogeneous genes in diagnosing lymph node metastasis.Methods:We selected five aberrant hypermethylated genes(AP2,CDH1,DACT2,HIN1，and RASF1A)in papillary thyroid carcinoma from the literature and the results of previous laboratory work.Tumor samples were collected from three different sites in the same tumor from 135 patients with papillary thyroid cancer.Methylation-specific PCR(MSP)was used to detect the methylation status of the above five genes in the samples,and the results of methylation detection in the three tissues were compared to determine whether the genes had intratumor DNA methylation heterogeneity.Chi-square analysis was applied to explore the relationship between the methylation heterogeneity and clinical factors,to preliminarily explore the factors affecting the DNA methylation heterogeneity,and to explore the correlation between intratumor methylation heterogeneity and lymph node metastasis.The heterogeneous methylated genes associated with lymph node metastasis were combined with other clinical indicators to determine lymph node metastasis.Receiver operating characteristic(ROC)curve was adopted and area under the curve(AUC)was applied to test the diagnostic efficacy.Results:The methylation rate of these genes was significantly increased after the synthesis of three tissues compared with that of single tissue.Intratumoral DNA methylation heterogeneity of 5 genes was widely present in papillary thyroid carcinoma.Methylation heterogeneity of AP2,CDH1,and DACT2 was significantly correlated with tumor size.CDH1 methylation heterogeneity was negatively correlated with lymph node metastasis.Through the analysis of clinical data,it was found that the age of patients and tumor size were the risk factors affecting lymph node metastasis.Combined with age,tumor size,and heterogeneous methylated CDH1,the AUC of lymph node metastasis was the highest,reaching 0.751.Conclusion:This study reveals that there are extensive DNA methylation changes and intratumor methylation heterogeneity in papillary thyroid carcinoma;there is a significant correlation between intratumor methylation heterogeneity and clinicopathological characteristics.When CDH1 has methylation heterogeneity,it can indicate that the risk of lymph node metastasis is reduced.In short,intratumoral DNA methylation heterogeneity may be one of the important perspectives to explain the diversity of biological behavior of thyroid cancer and it is worthy of further study.