PLAP (EP194)

Placental alkaline phosphatase (PLAP) is normally produced by primordial germ cells and syncytiotrophoblasts, and the detection of its expression has been useful in identifying germ cell tumors.1 Anti-PLAP antibody immunoreacts with germ cell tumors and can discriminate between these and other neoplasms. Somatic neoplasms e.g. breast, gastrointestinal, prostatic and urinary cancers may also immunoreact with antibodies to PLAP. Anti-PLAP positivity in conjunction with keratin negativity favors seminoma over carcinoma. Germ cell tumors are usually keratin positive, but they regularly fail to stain with anti-EMA, whereas most carcinomas stain with anti-EMA.2-7 Anti-PLAP has been useful in the diagnosis of gestational trophoblastic disease. Complete hydatidiform mole shows strong expression of hCG and weak expression of PLAP. Weak hCG and strong PLAP expression is found in partial hydatidiform mole. Choriocarcinoma presents strong expression of hCG and weak expression of hPL and PLAP.8 In addition to its role as a germ cell marker, PLAP may also be used as a myogenic marker in identifying soft tissue tumors.1