Alkaline phosphatase, placental-like (ALPG), also known as germ cell alkaline phosphatase (GCAP), is a glycosylphosphatidylinositol (GPI)-anchored enzyme encoded by the *ALPG* gene. It belongs to the alkaline phosphatase family, which catalyzes phosphate ester hydrolysis and plays roles in metabolism, mineralization, and cell signaling. ALPG is predominantly expressed in placental trophoblasts during embryogenesis but is also detected in germ cell tumors (e.g., seminomas, ovarian cancers) and some somatic cancers, making it a potential biomarker for malignancies. Its ectopic expression in cancers is linked to tumor progression, metastasis, and drug resistance.
ALPG-specific antibodies are critical tools for research and diagnostics. They enable the detection of ALPG in tissues (via immunohistochemistry) or serum (via ELISA), aiding in cancer subtype classification, prognosis assessment, and residual disease monitoring. In reproductive medicine, ALPG antibodies help study placental development and pregnancy-related disorders. Additionally, ALPG’s restricted expression in healthy tissues and prevalence in tumors have spurred interest in therapeutic applications. Antibody-drug conjugates (ADCs) or CAR-T therapies targeting ALPG are under exploration for precision oncology. However, cross-reactivity with other alkaline phosphatase isoforms (e.g., intestinal or tissue-nonspecific forms) requires rigorous antibody validation to ensure specificity.