**Core Concept**
Choriocarcinoma is a rare and aggressive type of gestational trophoblastic disease (GTD) that arises from the placental tissue. It is a malignant tumor that often presents with metastatic disease, making early detection crucial.

**Why the Correct Answer is Right**
The correct answer is linked to the pathophysiology of choriocarcinoma, which involves the abnormal proliferation of trophoblastic cells. A previous history of molar pregnancy is a well-established risk factor for developing choriocarcinoma. This is because molar pregnancies are characterized by the abnormal growth of trophoblastic cells, which can sometimes persist and progress to malignancy. The human chorionic gonadotropin (hCG) levels are often elevated in molar pregnancies, and this hormone can also serve as a tumor marker for choriocarcinoma.

**Why Each Wrong Option is Incorrect**
* **Option A:** A history of spontaneous abortion is not a risk factor for choriocarcinoma. While spontaneous abortions can be associated with various complications, the risk of developing choriocarcinoma is not increased.
* **Option B:** A history of ectopic pregnancy is not a direct risk factor for choriocarcinoma. However, ectopic pregnancies can be associated with other complications, such as infertility and increased risk of future ectopic pregnancies.
* **Option C:** A history of miscarriage is not a risk factor for choriocarcinoma. While miscarriages can be associated with various complications, the risk of developing choriocarcinoma is not increased.

**Clinical Pearl / High-Yield Fact**
A key clinical correlation is that choriocarcinoma often presents with elevated hCG levels, which can be used as a tumor marker for diagnosis and follow-up. This is especially important in cases where the tumor is not easily accessible for biopsy.

**Correct Answer: D. A previous history of molar pregnancy.**