## **Core Concept**
Ewing's sarcoma is a type of malignant bone tumor that primarily affects children and young adults. It is characterized by specific genetic mutations that contribute to its pathogenesis. The most common mutation involves a chromosomal translocation.

## **Why the Correct Answer is Right**
The correct answer, , involves the EWSR1 gene on chromosome 22 and the FLI1 gene on chromosome 11. This translocation, t(11;22)(q24;q12), results in the fusion of the EWSR1 gene with the FLI1 gene, creating an EWSR1-FLI1 fusion protein. This fusion protein acts as an aberrant transcription factor that promotes cell proliferation and inhibits differentiation, contributing to tumorigenesis. This specific translocation is found in approximately 85% of Ewing's sarcoma cases, making it the most common mutation in this type of cancer.

## **Why Each Wrong Option is Incorrect**
* **Option A:** - This option is incorrect because while other translocations can occur in Ewing's sarcoma, such as t(21;22) leading to an EWSR1-ERG fusion, they are less common than the t(11;22) translocation.
* **Option B:** - This option does not specify a known common mutation associated with Ewing's sarcoma.
* **Option C:** - Similarly, this option does not represent a well-documented mutation for Ewing's sarcoma.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that the presence of the EWSR1-FLI1 fusion protein, resulting from the t(11;22) translocation, is not only diagnostic but also a potential target for therapy. Molecular testing for this translocation can aid in the diagnosis of Ewing's sarcoma, especially in cases where histological features are atypical.

## **Correct Answer:** . EWSR1-FLI1 fusion due to t(11;22) translocation.