**Core Concept**
Prostate-specific antigen (PSA) is a protein produced by the prostate gland, and elevated levels of PSA in the blood can indicate prostate cancer, benign prostatic hyperplasia (BPH), prostatitis, or other conditions. The American Urological Association (AUA) recommends a PSA threshold of 4 ng/mL for further investigation, but a PSA level of >20 ng/mL is generally considered highly suggestive of prostate cancer.

**Why the Correct Answer is Right**
A PSA level of >20 ng/mL is associated with prostate cancer because it is a marker of prostate cell disruption, which can occur due to cancerous cell growth and tissue destruction. Prostate cancer cells can produce and secrete PSA into the bloodstream, leading to elevated levels. This is in contrast to BPH, where PSA levels are usually lower and more variable. Prostatitis can also cause elevated PSA levels, but the levels are typically lower than those seen in prostate cancer.

**Option A:** Prostate cancer is the correct answer because it is the most common cause of significantly elevated PSA levels (>20 ng/mL). While other conditions like BPH and prostatitis can cause elevated PSA, the levels are usually not as high as those seen in prostate cancer.

**Option B:** While BPH can cause elevated PSA levels, they are typically lower than 20 ng/mL and are often associated with a higher PSA density (PSAD). A PSA level of >20 ng/mL is not typical for BPH.

**Option C:** Prostatitis can cause elevated PSA levels, but these levels are usually lower than 20 ng/mL and are often accompanied by symptoms of infection such as fever, dysuria, and urinary frequency.

**Option D:** Metastatic carcinoma refers to cancer that has spread from one part of the body to another. While prostate cancer can metastasize to other parts of the body, the term "metastatic carcinoma" is not specific to prostate cancer and is not the best answer choice.

**Clinical Pearl / High-Yield Fact**
A PSA level of >20 ng/mL is considered highly suggestive of prostate cancer and warrants further investigation, including a digital rectal examination (DRE) and prostate biopsy.

**✓ Correct Answer: A. Prostate cancer**