- Placental site trophoblastic tumor (PSTT) is a rare form of gestational trophoblastic disease (GTD) that originates from the implantation site intermediate trophoblast. It accounts for about 1% of all GTDs, with an estimated incidence of 1 per 100,000 pregnancies. Most patients are in their thirties and the prevailing presenting symptom is abnormal vaginal bleeding. More than half of the patients present with disease limited to the uterus and the remainder present with disease extension beyond the uterus. The overall mortality rate is 25%. The most important adverse prognostic factor is disease extension beyond the uterus. Other adverse prognostic factors are interval from antecedent pregnancy > 2 years, mitotic count > 5 mitotic figures/10 high-power fields, and age > 40 years. Since PSTT is less sensitive to chemotherapy than GTDs originating from cytotrophoblast and syncytiotrophoblast (hydatidiform mole, invasive mole, and choriocarcinoma), hysterectomy is the mainstay of treatment. Systemic multi-agent chemotherapy is administered in the presence of disease extension beyond the uterus and considered in the presence of other adverse prognostic factors. The EP/EMA regimen seems to be the most effective chemotherapy available to date for PSTT. Although PSTT produces less human chorionic gonadotropin (hCG) than choriocarcinoma, beta-hCG is still the best available serum marker for monitoring the response to treatment and for follow-up.