APLN and central nervous system cancer: Pan‐cancer immune infiltration analysis revealed that apelin was in a negative correlation with CD8 T cells, NK cells, as well as macrophages within most tumours, except for lung squamous cell carcinoma (LUSC), low‐grade glioma (LGG), as well as pan‐kidney cohort (KIPAN) (Figure 9C), suggesting a potential role in immunosuppression within the TME.