An MRI pelvis with multiparametric imaging (T2, DWI, DCE) is performed on a 62-year-old man with elevated PSA (8.2 ng/mL) and abnormal digital rectal examination. A suspicious lesion showing restricted diffusion and early enhancement is identified in the structure marked **A** in the diagram. What is the most likely reason this zone is the most common site for prostate cancer detection?

Explanation

The peripheral zone (marked **A**) comprises approximately 70% of the prostate volume in healthy adults and is the anatomical origin of ~70% of prostate cancers. This zone is palpable on digital rectal examination as nodular induration when involved by malignancy. The high prevalence of cancer in this zone is both anatomical (large volume) and biological. Multiparametric MRI with PI-RADS scoring is the modern gold standard for detecting and characterizing lesions in the peripheral zone and guiding targeted biopsy. Understanding this zonal anatomy is critical for interpreting prostate imaging and risk stratification. **Why each distractor is wrong:** - **Transition zone origin**: The transition zone (~5% of normal prostate volume) is the site of benign prostatic hyperplasia (BPH), not malignant transformation. BPH causes lower urinary tract symptoms but is not a precursor to cancer. - **Central zone and ejaculatory ducts**: The central zone (~25% of volume) surrounds the ejaculatory ducts but accounts for only ~5% of prostate cancers. It is not the primary site of malignancy. - **Poor blood supply**: The peripheral zone actually has relatively good blood supply. Ischemic necrosis is not the mechanism of cancer development in this zone. **High-Yield:** Peripheral zone = 70% volume + 70% cancers; Transition zone = BPH; Central zone = ejaculatory ducts. mpMRI + PI-RADS guides biopsy and risk stratification. [cite: Harrison 21e Ch 87]