HMB 45 is tumor marker for ?
**Core Concept**
HMB-45 is a monoclonal antibody that specifically targets the protein product of the gene encoding the melanocytic differentiation antigen, also known as microphthalmia-associated transcription factor (MITF). This protein is highly expressed in melanocytic tumors and plays a crucial role in melanocyte development and differentiation.
**Why the Correct Answer is Right**
HMB-45 is widely used as a diagnostic marker for melanoma and other melanocytic lesions. The antibody recognizes the cytoplasmic protein product of the MITF gene, which is a transcription factor that regulates the expression of melanocyte-specific genes. In melanoma cells, the MITF protein is often overexpressed, making HMB-45 a useful marker for identifying these cells. The use of HMB-45 immunohistochemistry can help differentiate melanoma from other types of skin cancers, such as carcinomas and sarcomas.
**Why Each Wrong Option is Incorrect**
**Option A:** HMB-45 is not a marker for neuroendocrine tumors, which are typically stained with antibodies like chromogranin A or synaptophysin. Neuroendocrine tumors express different antigens that are not recognized by HMB-45.
**Option B:** HMB-45 is not a marker for lymphoid tumors, which are typically stained with antibodies like CD20 or CD3. Lymphoid tumors express different antigens that are not recognized by HMB-45.
**Option C:** HMB-45 is not a marker for epithelial tumors, which are typically stained with antibodies like cytokeratins or E-cadherin. Epithelial tumors express different antigens that are not recognized by HMB-45.
**Clinical Pearl / High-Yield Fact**
Remember that HMB-45 is a specific marker for melanocytic tumors, but it can also be expressed in other types of tumors, such as clear cell sarcoma and alveolar soft part sarcoma. A combination of immunohistochemical markers and clinical correlation is often necessary to establish a definitive diagnosis.
**Correct Answer:** C. Melanoma