Hepatocellular carcinoma (HCC) is the second most common cause of cancer-related death in the world. N 6 -methyladenosine (m 6 A) RNA methylation is dynamically regulated by m 6 A RNA methylation modulators ("writer," "eraser," and "reader" proteins), which are associated with cancer occurrence and development. The purpose of this study was to explore the relationships between m 6 A RNA methylation modulators and HCC. Methods: First, using data from The Cancer Genome Atlas (TCGA) and

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... al Cancer Genome Consortium (ICGC) databases, we compared the expression levels of 13 major m6A RNA methylation modulators between HCC and normal tissues. Second, we applied consensus clustering to the expression data on the m 6 A RNA methylation modulators to divide the HCC tissues into two subgroups (clusters 1 and 2), and we compared the clusters in terms of overall survival (OS), World Health Organization (WHO) stage, and pathological grade. Third, using least absolute shrinkage and selection operator (LASSO) regression, we constructed a risk signature involving the m 6 A RNA methylation modulators that affected OS in TCGA and ICGC analyses. Results: We found that the expression levels of 12 major m6A RNA methylation modulators were significantly different between HCC and normal tissues. After dividing the HCC tissues into clusters 1 and 2, we found that cluster 2 had poorer OS, higher WHO stage, and higher pathological grade. Four m 6 A RNA methylation modulators (YTHDF1, YTHDF2, METTL3, and KIAA1429) affecting OS in the TCGA and ICGC analyses were selected to construct a risk signature, which was significantly associated with WHO stage and was also an independent prognostic marker of OS. 3 Conclusions: In summary, m 6 A RNA methylation modulators are key participants in the malignant progression of HCC and have potential value in prognostication and treatment decisions. background According to the Cancer Statistics of China in 2015, hepatocellular carcinoma (HCC) is the second and fifth most common cause of cancer-related death in men and women, respectively [1].Worldwide, HCC is the most common type of primary liver cancer, ranking second among malignant tumors, with more than 700,000 deaths each year [2]. Chronic liver inflammation caused by hepatitis B virus (HBV), hepatitis C virus (HCV), or aflatoxin B1 is the main cause of HCC[3]. A series of treatments have been developed for patients with HCC, including surgery, chemotherapy, and radiotherapy. However, the mortality rate is still very high [4-6]. Understanding the molecular mechanisms underlying the development of HCC is essential to improve diagnostic tools and treatments. RNA methylation in mammalian cells is dynamic and reversible and has been suggested as another kind of epigenetic regulation analogous to DNA methylation or histone modification [7]. N 6 -methyladenosine (m 6 A) is considered the most frequent, abundant, and conserved internal modification of eukaryotic messenger RNA (mRNA) [8], microRNAs (miRNAs) [9], and long non-coding RNA [10]. The m 6 A modification occurs at a consistent motif, RRm 6 ACH([G/A/U][G>A]m 6 AC[U>A>C]) [11]. In addition, experiments using m 6 A-specific antibodies and high-throughput sequencing (HTSeq) revealed that m 6 A modifications mainly appear around termination codons, in 3'-untranslated regions, and in long internal exons [12] .