Placental site trophoblastic tumor is a form of gestational trophoblastic disease, which is thought to arise from intermediate trophoblast. It may secrete human placental lactogen (human chorionic somatomammotropin), and result in a false-positive pregnancy test. Immunohistochemistry: Often stains with hPL, keratin, Mel-CAM, EGFR. Prognosis : 10~20% of cases metastase leading to death. Treatment : Because chemotherapy is ineffective; the patient should undergo hysterectomy.