Final answer:
A choriocarcinoma typically occurs in molar pregnancies, which are abnormal growths of cells in the uterus.
Step-by-step explanation:
A choriocarcinoma typically occurs in molar pregnancies. A molar pregnancy is a type of pregnancy where there is an abnormal growth of cells in the uterus, instead of a normal pregnancy. Choriocarcinoma is a rare cancer that can develop from the tissue that forms during a molar pregnancy.