Background: Selenium (Se) exhibits its anti-carcinogenic properties by regulating the redox system. However, the relationship between selenoprotein P (SeP), mRNA (SELENOP  mRNA) and tumorigenesis remains unclear. Plasma SeP transports Se to various target tissues and has antioxidant characteristics. The present study aimed to explore the multifaceted pan-cancer properties of SELENOP  in terms of its tissue-specific expression, prognostic value, immune function, and signaling pathway enrichment.
Patients and Methods: The expression profile of SELENOP  was determined in 33 tumor types and survival, pathway enrichment, and correlation analyses were conducted based on TCGA database. The relationship between SELENOP  expression and immune infiltration and macrophage subtype gene markers was investigated using the TIMER and GEPIA.
Results: SELENOP  gene expression was decreased in many cancer tissues, but was upregulated in brain lower grade glioma (LGG). Furthermore, SELENOP  expression was associated with a better prognosis in most cancers, but a poorer prognosis in LGG and uterine corpus endometrioid carcinoma (UCEC). Our results showed that SELENOP  was correlated with infiltration level of six immune cell types, where SELENOP  also showed a strong correlation with macrophages in some cancer types. However, we failed to determine macrophage polarization in 33 tumor types. SELENOP  negatively regulated vascular endothelial cell proliferation in LGG and UCEC and epidermal cell differentiation in six tumor types. In contrast, upregulation was related to immune function, including T cell activation, B cell-mediated immunity, adaptive immune response and immune response regulation cell surface receptor signaling pathways in another six tumor types.
Conclusion: These findings highlighted the tissue-specific expression, prognostic value and immune characteristics of SELENOP  in pan-cancer, and provided insights for illustrating the role of SELENOP  in tumorigenesis.
Keywords: selenoprotein P, pan-cancer, immune infiltration, prognosis, tissue-specific expression