Human major histocompatibility complex (MHC) antigens, also referred to as human leukocyte antigens (HLA), are encoded by genes located on the short arm of chromosome 6 (6p21.3). HLA-G is a non-classical MHC class I molecule with multiple immunoregulatory properties. HLA-G exhibits a restricted pattern of expression that includes placental extravillous trophoblasts at the maternal-fetal interface, where it abolishes maternal immune cell activity against fetus and establishes immune tolerance. Aberrant expression of HLA-G has been found in a variety of human neoplastic diseases. It plays an important role in the escape of tumor cells from immunosurveillance.