A 48-year-old man complains of weakness and easy fatigability for 6 weeks. He has worked for 20 years in a chemical factory that produces a variety of plastics and other synthetic compounds. A complete blood count shows a hemoglobin level of 8.2 g/dL, WBC count of 45,000/mL, and a platelet count of 40,000/mL. Examination of a bone marrow aspirate reveals numerous malignant myeloblasts, and a diagnosis of acute myeloid leukemia is made. Exposure to which of the following agents is the most likely cause of this patient’s hematologic disease?

**Core Concept**
Occupational exposure to certain chemicals and organic compounds can increase the risk of developing acute myeloid leukemia (AML), a type of cancer that affects the blood and bone marrow. The patient's prolonged exposure to plastics and synthetic compounds in the chemical factory likely played a role in the development of his hematologic disease.

**Why the Correct Answer is Right**
The most likely cause of this patient's AML is benzene, a known human carcinogen that can cause bone marrow failure and increase the risk of developing leukemia. Benzene is a solvent used in the production of plastics, synthetic fibers, and other organic compounds. Exposure to benzene can lead to genetic mutations in the bone marrow cells, resulting in the development of malignant myeloblasts. The patient's prolonged exposure to benzene in the chemical factory likely caused the genetic damage that led to the development of his AML.

**Why Each Wrong Option is Incorrect**
* **Option A:** Styrene is another chemical used in the production of plastics, but it is not as strongly associated with the development of AML as benzene.
* **Option B:** Toluene is a solvent used in various industrial processes, but it is not as likely to cause AML as benzene.
* **Option D:** Formaldehyde is a known human carcinogen, but it is more commonly associated with the development of nasopharyngeal cancer and other types of cancer, rather than AML.

**Clinical Pearl / High-Yield Fact**
Benzene exposure can also lead to other hematologic abnormalities, including anemia, thrombocytopenia, and neutropenia. It is essential to consider occupational exposure to chemicals and organic compounds in the differential diagnosis of AML, especially in patients with a history of prolonged exposure.

**Correct Answer:** C. Benzene.

✓ Correct Answer: A. Benzene