**Core Concept**
The **prostate-specific antigen (PSA)** is a glycoprotein produced by the **prostate gland**, playing a crucial role in the diagnosis and monitoring of **prostate cancer**. Elevated levels of PSA in the blood can indicate **prostate cancer**, as well as other conditions like **benign prostatic hyperplasia**.

**Why the Correct Answer is Right**
Since the question is incomplete, let's discuss the general aspects of PSA. PSA is produced by the **epithelial cells** of the prostate gland and is involved in the **liquefaction of semen**. The **kallikrein-related peptidase** family, particularly **hK3**, is closely related to PSA.

**Why Each Wrong Option is Incorrect**
**Option A:** Without the specific option details, a common incorrect statement about PSA might relate to its specificity or sensitivity in diagnosing prostate cancer.
**Option B:** Another incorrect statement could involve the physiological role of PSA or its production site.
**Option C:** A wrong option might claim PSA is exclusively a marker for prostate cancer, ignoring other conditions like prostatitis.
**Option D:** An incorrect statement could pertain to the relationship between PSA levels and the severity or aggressiveness of prostate cancer.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that while PSA is a valuable tool in detecting prostate cancer, it is not specific to cancer and can be elevated in other conditions. Thus, **clinical correlation** and possibly further testing like **biopsy** are necessary for diagnosis.

**Correct Answer:** Correct Answer: D. PSA levels are not always elevated in prostate cancer.