Recognition of Tumor Cells:Tumor Antigens: Tumor cells often express abnormal proteins or altered levels of normal proteins that can serve as antigens.These tumor-associated antigens (TAAs) are recognized by the immune system as foreign.Major Histocompatibility Complex (MHC): Tumor antigens are presented on the surface of tumor cells by MHC molecules.This presentation is crucial for the activation of immune cells, particularly T cells.