This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Twin Pregnancy, Molar Pregnancy, Gestational Trophoblastic disease and contraception in special situations (Sour Grapes!), Subject name: Gynaecology & Obstetrics
Which of the following is the most common form of persistent trophoblastic disease that follows a non molar pregnancy? 
Select and explain. 
A. Choriocarcinoma, B. Invasive mole, C. Placental site trophoblastic tumor, D. Paial mole
A: Choriocarcinoma
Answer: A: Choriocarcinoma 
Explanation: 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: 2/3rd cases after normal delivery, 1/3rd 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.