Abstract: OBJECTIVE：To investigate changes in expression of alcohol dehydrogenase 1A (ADH1A) and association with microvascular invasion (MVI)，the tumor immune microenvironment and prognosis as molecular mechanisms for hepatocellular carcinoma (HCC). METHODS：Using publicly available proteomic data from 101 HCC patients，ADH1A expression between tumor tissues and adjacent non-tumor tissues was compared. Based on the median ADH1A protein expression level，patients were divided into high and low expression groups. Survival curves were plotted，and associations between ADH1A expression and clinicopathological features were analyzed. Gene Ontology (GO) biological process enrichment analysis was performed to identify pathways enriched among proteins positively or negatively correlated with ADH1A expression and to evaluate their abundance differences between high and low ADH1A expression groups. Immune infiltration was analyzed using the CIBERSORT algorithm to assess differences in immune cell subsets between groups. Spatial transcriptomics data were analyzed to explore the spatial expression pattern of ADH1A. Finally，Western blot and immunohistochemistry (IHC) were performed on clinical HCC tissue samples to examine ADH1A expression and its relationship with MVI status. RESULTS：ADH1A expression was significantly lower in tumor tissues compared to adjacent non-tumor tissues (P<0.01). Its expression was significantly associated with MVI (P<0.05)，and low ADH1A expression was strongly correlated with poor prognosis. GO enrichment analysis revealed that proteins positively correlated with ADH1A were mainly involved in metabolic processes such as organic acid metabolism，while negatively correlated proteins were enriched in cell-matrix adhesion and cell spreading pathways. Notably，seven key adhesion-related proteins within the “cell adhesion” biological process were significantly upregulated in the low ADH1A expression group (all P<0.05). Immune infiltration analysis showed that na-ve CD4 T cells and resting mast cells were significantly decreased in the low ADH1A group (both P<0.05). Spatial transcriptomics，Western blot，and IHC consistently demonstrated reduced ADH1A expression in tumor regions compared to non-tumor regions，and lower expression in MVI-positive samples than in MVI-negative ones. CONCLUSION：ADH1A was downregulated in hepatocellular carcinoma and was significantly associated with microvascular invasion and poor prognosis. ADH1A may exert anti-tumor effects by modulating cell adhesion pathways and the immune microenvironment，suggesting its potential as a prognostic biomarker and therapeutic target.

Key words: ADH1A, hepatocellular carcinoma, microvascular invasion, tumor immune microenvironment, cell adhesion pathways