All of the following immunohistochemical markers are positive in the neoplastic cells of granulocytic sarcoma, except –
**Core Concept**
Granulocytic sarcoma, also known as myeloid sarcoma, is a rare extramedullary tumor composed of immature granulocytic cells. It often arises in the setting of acute myeloid leukemia (AML) and can be associated with various immunohistochemical markers.
**Why the Correct Answer is Right**
Granulocytic sarcoma typically expresses markers associated with myeloid lineage, such as CD43, CD117 (c-KIT), and CD15. The neoplastic cells in granulocytic sarcoma may also express MPO (myeloperoxidase), which is a key enzyme in the maturation of myeloid cells. The presence of these markers helps differentiate granulocytic sarcoma from other types of tumors.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because CD43 is a common marker expressed in myeloid lineage cells, including granulocytic sarcoma.
**Option B:** This option is incorrect because CD117 (c-KIT) is a specific marker for myeloid cells and is often positive in granulocytic sarcoma.
**Option C:** This option is incorrect because MPO is a key enzyme in the maturation of myeloid cells and is commonly expressed in granulocytic sarcoma.
**Clinical Pearl / High-Yield Fact**
Granulocytic sarcoma can be a challenging diagnosis, but recognizing the characteristic immunohistochemical markers can help differentiate it from other types of tumors. A high index of suspicion is essential, especially in patients with AML or myeloproliferative neoplasms.
**Correct Answer:** D.