**Core Concept**
Choriocarcinoma is a type of gestational trophoblastic disease (GTD) that originates from the placental tissue. Metastatic choriocarcinoma refers to the spread of cancer cells to distant organs, such as the lungs. The ideal treatment for metastatic choriocarcinoma involves a combination of chemotherapy and close monitoring to prevent recurrence.

**Why the Correct Answer is Right**
The treatment of choice for metastatic choriocarcinoma is chemotherapy, specifically a combination of methotrexate and actinomycin-D. Methotrexate inhibits dihydrofolate reductase (DHFR), an enzyme essential for DNA synthesis and repair, thereby preventing cancer cell proliferation. Actinomycin-D, also known as dactinomycin, intercalates into DNA, inhibiting RNA synthesis and preventing cancer cell growth. This combination of chemotherapy agents has been shown to be highly effective in treating metastatic choriocarcinoma.

**Why Each Wrong Option is Incorrect**
* **Option A:** Radiation therapy may be used as an adjunct to chemotherapy in some cases, but it is not the ideal treatment for metastatic choriocarcinoma.
* **Option B:** Surgery may be considered for localized disease, but it is not effective for metastatic disease.
* **Option D:** Hormonal therapy is not a standard treatment for choriocarcinoma, which is a hormone-independent tumor.

**Clinical Pearl / High-Yield Fact**
Methotrexate is a key component of the treatment regimen for metastatic choriocarcinoma, and its effectiveness is often monitored through serial beta-hCG levels. A decrease in beta-hCG levels is a good indicator of response to treatment.

**Correct Answer: C. Methotrexate and actinomycin-D.**