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Yin Li,1,* Manling Jiang,2,3,* Yongqi Wei,1,* Xiang He,2 Guoping Li,2,* Chunlai Lu,1 Di Ge1 1Department of Thoracic Surgery, Zhongshan Hospital, Fudan University, Shanghai, People’s Republic of China; 2Laboratory of Allergy and Precision Medicine, Chengdu Institute of Respiratory Health, Affiliated Hospital of Southwest Jiaotong University, The Third People’s Hospital of Chengdu, Chengdu, Sichuan, People’s Republic of China; 3State Key Laboratory of Quality Research in Chinese Medicine, Macau University of Science & Technology, Taipa, Macao Special Administrative Region of China*These authors contributed equally to this workCorrespondence: Chunlai Lu; Di Ge, Email lu.chunlai@zs-hospital.sh.cn; ge.di@zs-hospital.sh.cnBackground: The pyrimidine salvage pathway plays a critical role in tumor progression and patient outcomes. The roles of pyrimidine salvage pathway-related genes (PSPGs) in cancer, however, are not fully understood. This study aims to depict the characteristics of PSPGs across various cancers.Methods: An integrative pan-cancer analysis of six PSPGs (CDA, UCK1, UCK2, UCKL1, UPP1, and UPP2) was conducted using TCGA data, single-cell RNA sequencing datasets, and patient samples. Single-cell transcriptome analysis and RT-qPCR were used to validate the relation between UPP1 and cytokines. Flow cytometry was performed to validate the role of UPP1 in immune checkpoint regulation. The correlation between UPP1 and tumor associated neutrophils (TAN) were investigated and validated by single-cell transcriptome analysis and tissue microarrays (TMAs).Results: PSPGs showed low mutation rates but significant copy number variations, particularly amplifications in UCKL1, UPP1, and UCK2 across various cancers. DNA methylation patterns varied, with notable negative correlations between methylation and gene expression in UPP1. PSPGs were broadly up-regulated in multiple cancers, with correlations to clinical staging and prognosis. Proteomic data further confirmed these findings. Functional analysis revealed PSPGs’ associations with tumor proliferation, metastasis, and various signaling pathways. UPP1 showed strong correlations with the tumor microenvironment (TME), particularly with cytokines, immune checkpoints, and various immune cells. Single-cell transcriptome analysis confirmed these associations, highlighting UPP1’s influence on cytokine expression and immune checkpoint regulation. In esophageal squamous cell carcinoma (ESCC), UPP1-high tumor cells were significantly associated with immunosuppressive cells in the TME. Spatial analysis using TMAs revealed that UPP1+ tumor cells were predominantly located at the invasive margin and closely associated with neutrophils, correlating with poorer patient prognosis.Conclusion: Our study depicted the multi-dimensional view of PSPGs in cancer, with a particular focus on UPP1’s role in the TME. Targeting UPP1 holds promise as a potential strategy for cancer therapy.Keywords: pyrimidine salvage pathways, UPP1, microenvironment