**Question:** A child presents with Ewing's sarcoma. Histology shows it as one of the small round blue cell tumors. Which of the following gets accumulated in the cells of Ewing's sarcoma?

A. Fluorodeoxyglucose (FDG)
B. Chromium-51
C. Technetium-99m
D. Thallium-201

**Correct Answer:** A. Fluorodeoxyglucose (FDG)

**Core Concept:** Ewing's sarcoma is a rare type of cancer that primarily affects bones and soft tissues. Histologically, it is characterized as a small round blue cell tumor. Ewing's sarcoma is known to have a specific genetic alteration involving the EWSR1-FLI1 fusion gene, which results in abnormal cell signaling and uncontrolled cell growth.

**Why the Correct Answer is Right:** FDG is a glucose analogue used in Positron Emission Tomography (PET) scans to visualize areas of high glucose utilization in the body. Ewing's sarcoma is characterized by high glucose uptake due to its aggressive nature and active cell division. Therefore, FDG gets accumulated in the cells of Ewing's sarcoma, making it the correct answer among the options provided.

**Why Each Wrong Option is Incorrect:**

B. Chromium-51: Chromium-51 is a radioactive isotope primarily used in nuclear medicine for bone scans or myocardial perfusion imaging. It is not a radiotracer for PET scans and does not accumulate in Ewing's sarcoma cells.

C. Technetium-99m: Technetium-99m is another radioactive isotope commonly used for bone scans, myocardial perfusion imaging, and single-photon emission computed tomography (SPECT) scans. It is not a suitable radiotracer for PET scans and does not accumulate in Ewing's sarcoma cells.

D. Thallium-201: Thallium-201 is a radioactive isotope primarily used for myocardial perfusion imaging and brain scans. Like Chromium-51 and Technetium-99m, it is not a suitable radiotracer for PET scans and does not accumulate in Ewing's sarcoma cells.

**Clinical Pearl:** PET scans using FDG are crucial in the diagnosis, staging, and monitoring response to treatment in Ewing's sarcoma. The increased glucose uptake by the tumor cells helps in identifying the tumor's location, extent, and response to therapy.