<prompt> Which of the following is the most common form of persistent trophoblastic disease that follows a non molar pregnancy?ChoriocarcinomaInvasive molePlacental site trophoblastic tumorPaial mole  <response>: Gestational trophoblastic neoplasia GTN Invasive mole: Develops after molar pregnancy only. Very rarely follows other gestations PSTT Placental Site Trophoblastic Tumor: may follow any type of gestation Choriocarcinoma: 23rd cases after normal delivery, 13rd cases after molar pregnancy Epitheloid Trophoblastic tumor: remote antecedant pregnancy NOTE: After a nonmolar pregnancy, persistent GTN always has the histologic pattern of choriocarcinoma. Histologic characterization of choriocarcinoma depends on sheets of anaplastic syncytiotrophoblast and cytotrophoblast without chorionic villi. The choriocarcinoma is classically a soft, fleshy, yellow-white tumour with a marked tendency to form large pale areas of ischemic necrosis, foci of cystic softening, and extensive haemorrhage. 