Okay, let's tackle this question. The user provided a scenario about a 72-year-old man with a prostate nodule and elevated PSA. The question is about the next step in investigation. First, I need to recall the standard diagnostic pathway for prostate issues, especially prostate cancer.

So, the core concept here is the evaluation of a suspicious prostate finding. Elevated PSA and a nodule on DRE are red flags for prostate cancer. The next step would usually be a biopsy to confirm malignancy. But wait, what's the exact next step after elevated PSA and abnormal DRE? I think it's a prostate biopsy, specifically transrectal ultrasound-guided biopsy.

Now, the options aren't listed, but the correct answer is likely C or D. Let me think about common options. In such cases, the next steps after DRE and PSA would be imaging like MRI or biopsy. However, MRI might not be the immediate next step. Typically, if PSA is elevated and DRE is abnormal, the gold standard is a biopsy. So the answer is probably a biopsy.

For the incorrect options, maybe they include options like CT scan, MRI, or bone scan. Those might be done later for staging but not the immediate next step. Also, maybe a repeat PSA isn't the next step. The clinical pearl here is that biopsy is the confirmatory test. So I need to structure the explanation around that.

**Core Concept**
The scenario involves a suspicious prostate nodule and elevated prostate-specific antigen (PSA), which are hallmark signs of **prostate cancer**. The next diagnostic step must confirm malignancy, requiring **histopathological evaluation** via biopsy.

**Why the Correct Answer is Right**
**Prostate biopsy** (specifically transrectal ultrasound-guided biopsy) is the definitive test to diagnose prostate cancer. Elevated PSA and abnormal digital rectal examination (DRE) findings (e.g., nodule, asymmetry) necessitate biopsy to obtain tissue for histological confirmation, including Gleason scoring to assess tumor aggressiveness.

**Why Each Wrong Option is Incorrect**
**Option A:** *CT scan* is not indicated early; it lacks sensitivity for small tumors and is used for staging advanced disease.
**Option B:** *MRI* may be used for risk stratification or to guide biopsy in select cases but is not the immediate next step.
**Option D:** *Bone scan* is reserved for patients with clinical suspicion of metastasis, not initial diagnosis.

**Clinical Pearl / High-Yield Fact**
Never skip **biopsy** when PSA is elevated and DRE is abnormal. Remember: **PSA + DRE = biopsy**. Avoid over-reliance on imaging for initial diagnosis.

**Correct Answer: C. Prostate biopsy**

✓ Correct Answer: D. Transrectal ultrasound-guided prostate biopsy