Placental alkaline phosphatase (PLAP) is a heat-stable isoenzyme belonging to the alkaline phosphatase family, primarily expressed in the placenta during pregnancy. It plays a role in nutrient absorption and cellular differentiation during embryogenesis. Structurally, PLAP is a glycosylphosphatidylinositol (GPI)-anchored membrane protein encoded by the ALPP gene on chromosome 2. While its expression diminishes in most adult tissues, trace levels may persist in the cervix, testes, and thymus.
Clinically, PLAP serves as a tumor marker due to its ectopic expression in various malignancies. It is notably elevated in germ cell tumors (e.g., seminomas, dysgerminomas) and certain carcinomas, including ovarian, gastrointestinal, and lung cancers. PLAP antibodies are widely employed in immunohistochemistry (IHC) to detect PLAP in tissue samples, aiding in differential diagnosis and tumor classification. However, its specificity is limited as PLAP may also be expressed in non-neoplastic conditions like inflammatory bowel disease.
Research continues to explore PLAP's role in cancer biology and its potential as a therapeutic target. Recent studies suggest its involvement in cell adhesion and drug resistance mechanisms. Despite advances, distinguishing PLAP from other alkaline phosphatase isoenzymes (e.g., intestinal or tissue-nonspecific types) remains crucial for accurate diagnostic interpretation.