CD-99 is the marker for:
**Core Concept**
The **CD markers** are a protocol used for the identification and investigation of cell surface molecules present on white blood cells, also known as leukocytes. **CD99** is one such marker, primarily expressed on the surface of certain cells, including some types of lymphocytes and tumor cells.
**Why the Correct Answer is Right**
**CD99** is particularly notable for its association with Ewing's sarcoma, a malignant bone tumor. It is used as a diagnostic marker to help differentiate Ewing's sarcoma from other types of tumors. The presence of **CD99** on the surface of tumor cells can aid in the diagnosis of this condition.
**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because it is not associated with **CD99**.
**Option B:** Incorrect as it does not relate to the specific marker **CD99**.
**Option C:** Incorrect because, although **CD99** is a marker, the correct association is not with this option.
**Clinical Pearl / High-Yield Fact**
A key point to remember is that **CD99** is highly expressed in Ewing's sarcoma, making it a crucial diagnostic tool.
**Correct Answer:** D. Ewing's Sarcoma.