## **Core Concept**
Gemtuzumab ozogamycin is an antibody-drug conjugate used in the treatment of certain types of leukemia. It targets a specific antigen on the surface of cancer cells. The drug consists of a monoclonal antibody linked to a cytotoxic agent.

## **Why the Correct Answer is Right**
The correct answer, **CD33**, is a surface antigen found on the majority of blast cells in acute myeloid leukemia (AML) and on some normal myeloid cells. Gemtuzumab ozogamycin specifically binds to CD33, delivering a cytotoxic payload that induces apoptosis in leukemic cells. This targeted approach aims to minimize damage to normal cells.

## **Why Each Wrong Option is Incorrect**
* **Option A:** Not specified - This option is incorrect because it does not accurately represent the target of gemtuzumab ozogamycin.
* **Option B:** Not specified - This option is incorrect as it does not correspond to the known target of gemtuzumab ozogamycin.
* **Option D:** Not specified - This option is incorrect because it does not correctly identify the antigen targeted by gemtuzumab ozogamycin.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that gemtuzumab ozogamycin was initially approved for the treatment of relapsed or refractory AML and later received accelerated approval for newly diagnosed AML in combination with chemotherapy. However, due to concerns about increased risk of death, its use has been restricted.

## **Correct Answer:** C. CD33.