Which of the following is HMB45 negative?
**Core Concept**
HMB45 is a monoclonal antibody used as a marker in immunohistochemistry to identify melanocytic lesions, particularly melanoma, due to its reactivity with an intermediate filament protein called gp100 or melanocyte-specific protein.
**Why the Correct Answer is Right**
HMB45 is a specific marker for melanocytic lesions, but it can also be positive in other tumors that express gp100, such as neuroendocrine tumors. However, certain tumors are known to be HMB45 negative, including lymphomas and carcinomas of various types. In contrast, HMB45 is typically strongly positive in melanomas and some other melanocytic lesions.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because while lymphomas can have a variety of immunophenotypic markers, they are generally not associated with gp100 expression and therefore are not typically HMB45 positive.
**Option B:** This option is incorrect because carcinomas, including lung and breast carcinomas, are not typically associated with gp100 expression and therefore are not typically HMB45 positive.
**Option C:** This option is incorrect because melanomas are typically strongly positive for HMB45 due to their expression of gp100.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that HMB45 is a sensitive but not specific marker for melanocytic lesions, and its positivity should be interpreted in conjunction with other immunohistochemical markers and clinical correlation.
**Correct Answer:** D.