**Question:** Which of the following childhood tumors show extracranial metastasis?

A. Medulloblastoma
B. Ewing's sarcoma
C. Rhabdomyosarcoma
D. Retinoblastoma

**Core Concept:** Extracranial metastasis in childhood tumors refers to the spread of cancer cells from their primary site to other parts of the body. This can occur through blood or lymphatic vessels, and it is a concerning aspect of tumor progression as it can lead to increased morbidity and mortality.

**Why the Correct Answer is Right:**

Correct Answer: **D. Retinoblastoma**

Retinoblastoma is a rare cancer that originates in the developing retina of the eye. It typically occurs in children under five years old and is caused by mutations in the RB1 gene, which results in uncontrolled cell growth and formation of tumors. While retinoblastoma primarily affects the eye, the tumor can spread to extracranial sites through the bloodstream, leading to distant organ involvement.

**Why Each Wrong Option is Incorrect:**

A. Medulloblastoma: This is a type of brain tumor that primarily affects the cerebellum. Extracranial involvement is less common in medulloblastoma, although it can occur in advanced cases.

B. Ewing's sarcoma: Ewing's sarcoma is a rare bone and soft tissue cancer. While it can spread to adjacent tissues, extracranial involvement is less common compared to other options.

C. Rhabdomyosarcoma: This is a type of soft tissue sarcoma that can involve the head and neck region, but extracranial involvement is less common compared to retinoblastoma.

**Clinical Pearl:**

Understanding the extracranial potential of different childhood tumors is crucial for early detection, diagnosis, and treatment planning. In retinoblastoma, extracranial spread can lead to distant organ involvement, which requires a comprehensive evaluation and systemic therapy. Early diagnosis and treatment of extracranial spread can improve outcomes in these patients.