CD99 and cancer: These pathways are crucial for immune regulation in cancers: MHC-I and MHC-II facilitate antigen presentation to cytotoxic and helper T cells, respectively [43]; SELL and CD99 mediate leukocyte adhesion and trafficking, promoting immune cell migration [44]; Semaphorins modulate immune cell activation and movement beyond their classical roles in axon guidance [45]; NOTCH signaling influences immune cell differentiation and checkpoint regulation [46]; and CEACAM molecules act as immune checkpoints that may support immune evasion by cancer cells [47].