HMB 45 is a marker for –
**Core Concept**
HMB 45 (Human Melanoma Black 45) is a monoclonal antibody that targets an antigen present in melanocytic tumors, specifically melanoma cells. This marker is used in immunohistochemistry to help diagnose and differentiate melanocytic lesions from other skin lesions.
**Why the Correct Answer is Right**
HMB 45 reacts with an intermediate filament protein called gp100, which is expressed in melanocytes and melanoma cells. The gp100 protein is involved in the processing and presentation of antigens to the immune system, making it a useful target for immunotherapy and diagnostic markers. HMB 45 staining is typically positive in melanoma cells, which helps to distinguish them from other types of skin lesions.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because HMB 45 is not typically used to mark neural crest-derived tumors, such as neuroblastoma or pheochromocytoma.
**Option B:** This option is incorrect because HMB 45 is not a marker for epithelial cells, such as those found in carcinomas or adenocarcinomas.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that HMB 45 is a marker for melanoma cells, but it can also be positive in other types of melanocytic lesions, such as dysplastic nevi and Spitz nevi. However, the intensity and distribution of staining can help to differentiate between these lesions.
**Correct Answer: C. Melanoma cells.**