探讨黑色素瘤细胞黏附分子（MCAM）在肝细胞癌（肝癌）中表达、生物功能、临床相关性及其在患者生存预后、免疫治疗反应中作用。

从TCGA、UCSC，Xena和GEO数据库中检索MCAM mRNA表达数据和临床信息。使用ggplot2进行差异表达分析。使用“survival”和“survminer”R包进行生存分析。MCAM蛋白表达通过临床蛋白质组学肿瘤分析联盟（CPTAC）数据库进行评估。通过LinkedOmics进行基因本体（GO）功能和KEGG通路富集分析。使用单样本基因集富集分析（ssGSEA）和TIMER数据库评估免疫细胞浸润和免疫检查点关系。通过临床标本进行免疫组化验证。利用BEST数据库预测免疫治疗反应。

基于TCGA-LIHC数据集、GEO数据库、UALCA、CPTACP数据库的多组学分析显示，肝癌组织MCAM高表达。TCGA-LIHC数据集中MCAM高表达患者总体生存期（OS）及无进展生存期（PFS）明显低于低表达患者（HR=0.70，0.68；P<0.05）。GSE144269及GSE54236中高表达MCAM患者OS明显低于低表达患者（HR=0.67，0.72；P<0.05）。UALCA数据库分析显示，高表达MCAM患者与肝癌临床分期、肿瘤分级和淋巴结转移呈正相关（P<0.05）。MCAM表达在TCGA-LIHC数据集ROC曲线下面积（AUC）为0.921，95%CI：0.887~0.954，MCAM具有良好的诊断效能。GO功能和KEGG通路富集分析显示，MCAM共表达基因参与免疫反应通路，包括Th1/Th2细胞分化。MCAM高表达明显影响免疫细胞浸润水平及参与多种促癌信号通路。免疫组化证实肝癌组织中MCAM蛋白水平高表达。BEST分析表明，MCAM高表达可能预测对PD-1、PD-L1和CTLA-4靶向治疗的更好反应。

肝癌中MCAM高表达，其高表达与患者不良预后和免疫调节相关，MCAM可作为癌症预后的有价值生物标志物和免疫治疗疗效的潜在预测因子。

To investigate the expression, biological function and clinical relevance of melanoma cell adhesion molecule (MCAM) in hepatocellular carcinoma (HCC), and its role in the survival prognosis and immunotherapy response of HCC patients.

The MCAM mRNA expression level and clinical information were retrieved from TCGA, UCSC Xena and GEO databases. Differential expression analysis was performed using ggplot2. The "survival" and "survminer" R packages were used for survival analysis. The expression of MCAM protein was evaluated by the data base of Clinical Proteomic Tumor Analysis Consortium (CPTAC). Gene ontology (GO) functional and KEGG pathway enrichment analyses were conducted by LinkedOmics. Single-sample gene set enrichment analysis (ssGSEA) and TIMER database were used to evaluate the relationship between immune cell infiltration and immune checkpoints. Immunohistochemical assay was validated by using clinical samples. The response to immunotherapy was predicted by the BEST database.

Multiomics analysis based on the TCGA-LIHC data set, GEO, UALCA and CPTACP databases showed that MCAM was highly expressed in HCC tissues. In TCGA-LIHC data set, the overall survival (OS) and progression-free survival (PFS) of patients with high expression of MCAM were significantly lower than those with low MCAM expression (HR=0.70, 0.68; both P<0.05). In GSE144269 and GSE54236 databases, the OS of patients with high expression of MCAM was lower than that of patients with low MCAM expression (HR=0.67, 0.72; both P<0.05). UALCA database demonstrated that high expression of MCAM in HCC patients was positively correlated with clinical stage, tumor grade and lymph node metastasis (all P<0.05). In TCGA-LIHC data set, the area under the ROC curve (AUC) of MCAM expression was 0.921 (95%CI: 0.887-0.954), indicating that MCAM had high diagnostic efficiency. GO functional and KEGG pathway enrichment analyses showed that the co-expressed genes of MCAM participated in the immune response pathway, including Th1/Th2 cell differentiation. High MCAM expression significantly affected the level of immune cell infiltration and participated in multiple cancer-promoting signal pathways. Immunohistochemistry found high expression of MCAM protein in HCC tissues. BEST analysis demonstrated that high MCAM expression might predict better response to targeted therapy of PD-1, PD-L1 and CTLA-4.

MCAM is highly expressed in HCC, which is associated with poor prognosis and immune regulation of HCC patients. MCAM can be used as a valuable biomarker for cancer prognosis and a potential predictor for clinical efficacy of immunotherapy.