MIC-2 is a marker of –
**Core Concept**
MIC-2 is a gene that encodes the CD99 protein, which is a cell surface antigen involved in cell adhesion and signaling. It is a marker of Ewing's sarcoma, a type of malignant bone tumor.
**Why the Correct Answer is Right**
MIC-2/CD99 is expressed on the surface of Ewing's sarcoma cells, making it a useful diagnostic marker for this tumor type. Immunohistochemical staining for MIC-2/CD99 is often used in conjunction with other diagnostic techniques, such as cytogenetics and molecular genetics, to confirm the diagnosis of Ewing's sarcoma. The CD99 protein plays a role in cell-cell adhesion and signaling, and its expression is thought to contribute to the aggressive behavior of Ewing's sarcoma cells.
**Why Each Wrong Option is Incorrect**
**Option A:** Not a marker of Ewing's sarcoma, as MIC-2/CD99 is not typically expressed on the surface of other tumor cells, including osteosarcoma and chondrosarcoma.
**Option B:** While MIC-2/CD99 is a cell surface antigen, it is not a marker of neuroblastoma, which is characterized by the expression of other proteins, such as N-myc and synaptophysin.
**Option C:** Not a marker of rhabdomyosarcoma, as MIC-2/CD99 is not typically expressed on the surface of rhabdomyosarcoma cells, which are characterized by the expression of other proteins, such as desmin and myogenin.
**Clinical Pearl / High-Yield Fact**
When diagnosing Ewing's sarcoma, it is essential to consider the combination of clinical, radiographic, and histopathological findings, as well as immunohistochemical staining for MIC-2/CD99 and other diagnostic markers.
**Correct Answer:** C.