As a frequent type of malignant tumor, esophageal cancer (EC) is the sixth dominant source of cancer-related mortality globally, with 400,000 deaths annually [1]. The five-year survival rates for EC are in the range of 19–36% [[2], [3], [4]]. In Asia, the prevalent histologic type of EC is esophageal squamous cell carcinoma (ESCC), which is characterized by high mortality [5]. The absence of specific and novel therapeutic targets and prognostic biomarkers for ESCC poses a primary challenge in prolonging survival and enhancing quality of life for individuals with this disease [2].

The folate cycle plays a critical role in several cellular physiologies and pathologies, including the maintenance of biosynthesis of nucleotides, redox status and methylation reactions [6,7]. A recent meta-analysis of RNA-seq (RNA sequencing technology) data from tissue microarrays (TMAs) comprising approximately 1900 tumor tissues spanning 19 major kinds of tumors showed that mitochondrial folate metabolism is the most dysregulated metabolic pathway in various human cancers [8].

The folate pathway serves a critical role in one-carbon metabolism reactions, and multiple enzymes are required to maintain this complicated metabolic network [9,10]. Notably, the key enzymes in managing the folate pathway are MTHFD2, SHMT2 and MTHFD1L [11]. Among them, MTHFD2 and SHMT2 have been reported to have therapeutic potential in tumors [12,13], but evidence regarding the role of MTHFD1L in tumor development is ambiguous. MTHFD1L is essential in the folate pathway by catalyzing the last step of the reaction to generate formate, which enters the cytoplasmic folate cycle subsequently and is applied as a source of one-carbon donor molecules [11]. Previous literature reports MTHFD1L is highly expressed in Alzheimer's disease, neural tube defects, and coronary artery disease [14,15]. Our prior study illustrated that MTHFD1L is highly expressed in ESCC [16]. In this research, we explored its role in the regulation of metastasis of ESCC cells and its prognostic value in ESCC patients.