CD4 and neoplasm: Consistent with previous studies demonstrating its close association with tumor progression, prognosis, and responsiveness to immunotherapy [31,32,33,34], our analysis using the TIMER database revealed that HTR1F expression is strongly correlated with the infiltration of diverse immune cell subsets—including B cells, CD4+ and CD8+ T cells, neutrophils, macrophages, and dendritic cells—across 34 cancer types.