placental site trophoblastic tumor placental site trophoblastic tumor placental site trophoblastic tumor is a form of gestational trophoblastic disease, which is thought to arise from intermediate trophoblast. placental site trophoblastic tumorphotomicrograph showing proliferating intermediate trophoblast with scarce cytotophoblastic and syncytiotrophoblastic elementsspecialtyoncology, obstetrics the tumor may secrete human placental lactogen, and result in a false-positive pregnancy test. a placental site trophoblastic tumor is a monophasic neoplasm of the implantation site intermediate trophoblast, and usually a benign lesion, which comprises less than 2% of all gestational trophoblastic proliferations. preceding conditions include molar pregnancy (5%). compared to choriocarcinoma or invasive mole, hemorrhage is less conspicuous and serum β-hcg level is low, making early diagnosis difficult. immunohistochemistry: often stains with hpl, keratin, mel-cam, egfr. treatment because chemotherapy is ineffective; the patient should undergo hysterectomy. prognosis 10–20% of cases metastasize leading to death.