CD-99 is marker of :
**Core Concept**
CD-99, also known as MIC2, is a cell surface glycoprotein that serves as a marker for Ewing's sarcoma, a type of malignant bone tumor. It is a member of the immunoglobulin superfamily and plays a crucial role in cell adhesion and signaling.
**Why the Correct Answer is Right**
CD-99 is highly expressed on the surface of Ewing's sarcoma cells, making it a valuable diagnostic marker for this tumor type. The MIC2 gene, which encodes CD-99, is involved in the development and progression of Ewing's sarcoma. CD-99 is also used as a target for immunotherapy in some cases. The expression of CD-99 is not limited to Ewing's sarcoma, but it is highly specific for this tumor type.
**Why Each Wrong Option is Incorrect**
**Option A:** CD-99 is not a marker for neuroblastoma, which is typically associated with the expression of other markers such as NSE and chromogranin.
**Option B:** CD-99 is not a marker for rhabdomyosarcoma, which is typically associated with the expression of markers such as desmin and myogenin.
**Option C:** CD-99 is not a marker for osteosarcoma, which is typically associated with the expression of markers such as osteocalcin and collagen type I.
**Clinical Pearl / High-Yield Fact**
CD-99 is a valuable diagnostic marker for Ewing's sarcoma, and its expression is highly specific for this tumor type. Immunohistochemical staining for CD-99 is often used in conjunction with other diagnostic tests to confirm the diagnosis of Ewing's sarcoma.
**Correct Answer: C. CD-99 is a marker of Ewing's sarcoma.**