Oral cancer is one of the ten most common malignant tumors in the world, accounting for 5% of systemic malignancies, 90% of which are epithelial-derived squamous cell carcinoma [
1]. In recent years, the incidence of oral squamous cell carcinoma (OSCC) is increasing and the age of onset is getting younger [
2]. Quamous cell carcinoma, abbreviated as squamous cell carcinoma, also known as epidermal carcinoma, is a malignant tumor that occurs in the epidermis or accessory cells. The cancer cells have different degrees of keratinization, and are more common in areas covered with squamous epithelium, such as skin, mouth, lips, esophagus, cervix, vagina, etc. [
3]. OSCC is a common malignant tumor of the head and neck. The World Health Organization predicts that the incidence of OSCC will continue to rise in the next decade, and OSCC has become a disease with high morbidity and mortality. The world public health problem encourages people to further study the factors that influence the prognosis of the disease [
4]. Despite significant advances in cancer research over the past few decades, OSCC is still a worldwide malignancy. Usually, cancer begins with a single cell mutation in a somatic cell that leads to further proliferation, which activates the protooncogene and becomes an oncogene [
5]. Immunohistochemistry has been used to detect potential markers of head and neck tumors, which contribute to the diagnosis and prognosis of the disease. Epigenetic modification refers to a change in the expression and function of a gene without a change in the DNA sequence and a heritable phenotype. It plays an important role in gene expression, regulation, and inheritance, and plays an important role in the process of tumorigenesis. The regulatory mechanisms of epigenetic modification are methylation of DNA, methylation and acetylation of histones, and regulation of non-coding RNA [
6]. Epigenetic modification can lead to silencing or activation of genes. If epigenetic modification abnormalities in somatic cells lead to abnormal expression of certain genes, such as oncogene activation and tumor suppressor gene inactivation, abnormal proliferation of somatic cells. Recent studies have also shown that the occurrence of many malignant tumors is closely related to the epigenetic disorder of the cellular genome. This also provides new ideas for the study of molecular markers and therapeutic targets for malignant tumors at the epigenetic level [
7]. The diagnosis of previous oral cancer is mainly based on clinical manifestations, imaging, tumor marker levels or biopsy, and tumors have formed at the time of diagnosis [
8]. However, normal cells have developed signs of malignant transformation before the formation of tumors. If the epigenetic test is performed on the tissues, prediction or diagnosis can be made at an early stage or even before the cancer, and early prevention or treatment can improve the survival rate and improve the prognosis [
9]. One study generated stable head and neck squamous cell carcinoma (HNSCC) cell lines ectopically expressing the c-Fosgene. Exogenous expression of c-Fos in nontumorigenic MDA1386Tu cells makes these cells tumorigenic in nude mice. Furthermore, subcutaneous transplantation of c-Fos-overexpressing Cal27 cells (tumorigenic) into immunocompromised mice enhanced tumor growth as compared with parental cells. Mechanistic investigations demonstrated that c-Fos overexpression enhanced the epithelial–mesenchymal transition state and expression of CSC markers (Nanog, c-Myc, Sox2, and Notch1). Ectopic expression of c-Fos in HNSCC cells also displays increased sphere formation. We further observed that overexpression of c-Fos increased the expression of pERK and cyclin D1 in HNSCC cells [
10].
Since its discovery, the RASSF-1A gene has been extensively studied. A number of studies have shown that RASSF-1A is expressed almost in normal tissues and organs, but there are expression defects in various solid tumors [
11]. OSCC is a multi-factor participation, a common malignant tumor with multiple genes, and the inactivation and loss of tumor suppressor genes are closely related to its occurrence and development [
12]. The study found that the heterozygous loss of alleles often occurs in the short arm of chromosome 3 in OSCC. It is speculated that there may be tumor suppressor genes related to OSCC in chromosome 3p21. RASSF1 was reported from chromosome 3p21.3 locus novel candidate tumor suppressor gene [
13]. It has a variety of different mRNA splicing bodies, RASSF1A is one of the main ones, which is positive 100% expression in normal tissues, but often expressed in lung cancer, breast cancer, nasopharyngeal cancer, kidney cancer, prostate cancer and bladder cancer. The main mechanism of aberrant methylation of the RASSF1A gene in the 5′ CpG island of promoter has been found in a variety of tumors, but there are few reports about RASSF1A gene methylation status and transcriptional level expression in oral precancerous lesions and squamous cell carcinoma [
14]. This study was designed to investigate the expression of RASSF-1A in OSCC and adjacent tissues, and to investigate the mechanism of RASSF-1A gene in OSCC carcinogenesis, which looks for new directions for the treatment of OSCC.