**Core Concept**
Choriocarcinoma is a type of gestational trophoblastic disease (GTD) characterized by the malignant proliferation of trophoblastic cells. It is often associated with an abnormal trophoblastic cell population that does not undergo normal differentiation, leading to uncontrolled cell growth and tumor formation.

**Why the Correct Answer is Right**
The presence of beta-human chorionic gonadotropin (β-hCG) in the urine and serum is a hallmark of choriocarcinoma. β-hCG is a hormone produced by the placenta during pregnancy, and its levels typically decrease after delivery. However, in choriocarcinoma, the tumor cells produce excessive amounts of β-hCG, leading to elevated levels in the patient's blood and urine. This is because the tumor cells are able to produce β-hCG in an unregulated manner, resulting in persistently elevated levels.

**Why Each Wrong Option is Incorrect**
**Option A:** Elevated levels of alpha-fetoprotein (AFP) are more commonly associated with germ cell tumors, such as yolk sac tumors, rather than choriocarcinoma.
**Option B:** Elevated levels of lactate dehydrogenase (LDH) can be seen in a variety of malignancies, but it is not specific for choriocarcinoma.
**Option C:** The presence of a pelvic mass may be seen in various gynecological conditions, including ovarian and endometrial cancers, but it is not diagnostic of choriocarcinoma.

**Clinical Pearl / High-Yield Fact**
Choriocarcinoma is often associated with a history of molar pregnancy, abortion, or ectopic pregnancy, and patients may present with symptoms such as vaginal bleeding, pelvic pain, or abdominal distension.

**Correct Answer:** B. Elevated β-hCG levels.