Which of the following marker is used to diagnose rhabdomyosarcoma?
**Core Concept**
Rhabdomyosarcoma is a type of soft tissue sarcoma that arises from skeletal muscle progenitor cells. The diagnosis of this malignancy relies on a combination of clinical evaluation, imaging studies, and histopathological examination.
**Why the Correct Answer is Right**
Desmin is a muscle-specific protein that is expressed in skeletal and cardiac muscle cells. It is a sensitive marker for diagnosing rhabdomyosarcoma, as the tumor cells in this malignancy exhibit aberrant expression of desmin. This aberrant expression is due to the disruption of normal muscle cell differentiation pathways, leading to the production of immature muscle proteins like desmin.
**Why Each Wrong Option is Incorrect**
**Option A:** Myogenin is a transcription factor involved in muscle cell differentiation, but it is not a specific marker for rhabdomyosarcoma. While myogenin is expressed in some rhabdomyosarcoma cases, its absence does not rule out the diagnosis.
**Option B:** S-100 protein is a marker for melanocytic lesions and some types of soft tissue tumors, but it is not specific for rhabdomyosarcoma.
**Option C:** Cytokeratin is a marker for epithelial cells, and its expression is not typically seen in rhabdomyosarcoma.
**Clinical Pearl / High-Yield Fact**
Rhabdomyosarcoma is the most common soft tissue sarcoma in children, and its diagnosis requires a combination of clinical, radiological, and histopathological evaluation. Immunohistochemical staining for desmin is a useful adjunct in identifying this malignancy.
**Correct Answer: C. Desmin**