**Core Concept**
Retinoblastoma is a malignant tumor of the retina, primarily affecting children. In cases of advanced or metastatic disease, treatment aims to control tumor growth and prevent further spread. Chemotherapy is a systemic approach that targets cancer cells throughout the body.

**Why the Correct Answer is Right**
Chemotherapy is the preferred treatment for metastatic retinoblastoma due to its ability to reach and destroy cancer cells that have spread beyond the primary tumor site. This approach can be administered intravenously or directly into the cerebrospinal fluid to target tumor cells in the central nervous system. Chemotherapy agents, such as carboplatin and etoposide, work by interfering with DNA replication and cell division, ultimately leading to tumor cell death.

**Why Each Wrong Option is Incorrect**
**Option B:** Enucleation (removal of the eye) is typically reserved for cases where the tumor is localized within the eye and cannot be salvaged with other treatments. It is not suitable for metastatic disease.
**Option C:** Radiotherapy can be used to treat retinoblastoma, but it is generally reserved for localized disease or as an adjunct to chemotherapy. In the case of metastatic disease, chemotherapy is the primary treatment.
**Option D:** Cryotherapy involves freezing the tumor cells to induce cell death. While it can be used to treat small, localized tumors, it is not effective for metastatic disease.

**Clinical Pearl / High-Yield Fact**
For patients with retinoblastoma, early detection and treatment are critical. A thorough understanding of the disease's genetic basis and the importance of family history can aid in prompt diagnosis and appropriate treatment planning.

**✓ Correct Answer: A. Chemotherapy**