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
[{'content': 'Most common site of metastasis of choriocarcinoma is: \nSelect and explain. \nA. Lung, B. Liver, C. Vagina, D. Bone', 'role': 'user'}, {'content': 'Answer: A \nExplanation: FIGO- staging of gestational trophoblastic disease: Stage 1 - disease confined to uterus Stage 2 - disease extending outside the uterus but confined to genital structures (adnexa, vagina, broad ligaments) Stage 3 - disease extending to the lung, with or without known genital tract involvement Stage 4 - disease at other metastatic sites most common site of metastasis of choriocarcinoma is lung and is classified as stage 3', 'role': 'assistant'}]