PurposeThe characteristic of RENT3B in cancer remains ambiguous. We aimed to study the relationship between RENT3B and immune infiltration in liver hepatocellular carcinoma (LIHC) and lung squamous cell carcinoma (LUSC).Patients and methodsWe investigated the expression levels of RENT3B using ONCOMINE and TIMER databases, and assessed the interrelationship between RENT3B expression and survival using PrognoScan, GEPIA, and Kaplan–Meier plotter. Additionally, we examined the association between RENT3B and immune cells in the tumor microenvironment (TME), as well as markers of immune cells, using TIMER. Subsequently, we performed prognostic analysis based on the expression level of RENT3B within specific immune cell subgroups. Furthermore, we evaluated the promoter methylation profile of RENT3B between tumor and normal tissues in LIHC and LUSC using the DNMIVD database.ResultsRENT3B exhibited increased levels in both in LIHC and LUSC. High RENT3B expression was associated with unfavorable prognosis in LIHC, whereas it indicated a beneficial prognosis in LUSC. In LIHC, the expression of RENT3B positively correlated with immune infiltration levels of B cells, CD4 + T cells, CD8 + T cells, neutrophils, macrophages, and dendritic cells. However, in LUSC, the expression of RENT3B showed a negative correlation with immune infiltration levels of B cells, CD8 + T cells, neutrophils, macrophages, and dendritic cells. RENT3B exhibited positive correlations with 42 immune markers in LIHC, while it displayed negative associations with 10 immune markers in LUSC. Despite variations in immune cell enrichment and reduction subgroups, high RENT3B expression consistently indicated poor prognosis in LIHC, whereas it remained favorable in LUSC. Additionally, there were no significant differences observed in RENT3B promoter methylation between tumor and normal tissues in both LIHC and LUSC.ConclusionRENT3B can affect the overall tumor prognosis and is associated with immune infiltration, especially in LIHC and LUSC. Consequently, RENT3B can become a prognostic biomarker for LIHC and LUSC.