A 58-year-old man presents to the emergency depament with severe back pain. His history is negative for trauma and he has no other complaints. He denies urinary frequency, hesitancy, or dysuria. A digital rectal examination confirms the presence of a firm, hard, asymmetrical and stony prostate, suggestive of prostatic malignancy. In addition to PSA, which of the following markers can be demonstrated in the tumour cells?

## **Core Concept**
The question tests knowledge of prostate cancer markers. Prostate cancer often presents with elevated Prostate-Specific Antigen (PSA) levels, but the question asks for another marker associated with tumor cells.

## **Why the Correct Answer is Right**
The correct answer, **PSA (Prostate-Specific Antigen)**, is a well-known marker for prostate cancer. However, the question seems to be pointing towards another specific marker. Given the context, **Prostate-Specific Membrane Antigen (PSMA)**, also known as **glutamate carboxypeptidase II (GCPII)**, is highly expressed in prostate cancer cells, especially in metastatic and hormone-refractory disease. PSMA is used as a target for imaging and therapeutic interventions in prostate cancer.

## **Why Each Wrong Option is Incorrect**
- **Option A:** Without the specific details of option A, it's challenging to provide a direct explanation. However, common tumor markers like carcinoembryonic antigen (CEA) are not specific to prostate cancer.
- **Option B:** Similarly, without specifics, one can infer that markers not specifically associated with prostate cancer or not as directly linked to tumor cells in this context would be incorrect.
- **Option C:** This could potentially be a correct marker, but without specifics, it's hard to assess. Markers like **alpha-fetoprotein (AFP)** are more commonly associated with testicular cancer or hepatocellular carcinoma.
- **Option D:** Assuming this is not the correct answer, if it's a marker not specifically linked to prostate cancer cells or not commonly used in this context, it would be incorrect.

## **Clinical Pearl / High-Yield Fact**
A significant clinical pearl is that **PSMA** is not only a diagnostic marker but also a therapeutic target. Prostate cancer cells, especially in advanced stages, show high expression of PSMA, making it a valuable target for **Lu-177 DOTATATE** or **Lu-177 PSMA** therapy, which is a form of radioligand therapy.

## **Correct Answer:** .

✓ Correct Answer: A. AMACR