## Why option 2 is correct The peripheral zone (marked **A**) comprises approximately 70% of the prostate gland and is the anatomical origin of ~70% of prostate adenocarcinomas. Critically, the peripheral zone is located posteriorly and is directly palpable on DRE, allowing clinicians to detect nodular or asymmetric induration as a sign of malignancy. This anatomical accessibility explains why DRE remains a key screening tool for prostate cancer detection. The clinical anchor is that peripheral zone cancers present as palpable nodules on DRE, distinguishing them from benign prostatic hyperplasia (BPH), which arises in the transitional zone around the urethra and causes obstructive symptoms without being directly palpable on DRE (Robbins 10e Ch 21; Harrison 21e Ch 87). ## Why each distractor is wrong - **Option 1**: This describes the transitional zone (marked **B**), which is the site of origin for benign prostatic hyperplasia (BPH), not adenocarcinoma. BPH causes obstructive urinary symptoms but is not the predominant site of malignant transformation. - **Option 3**: This describes the central zone (marked **C**), which surrounds the ejaculatory ducts. Although the central zone can occasionally be involved in prostate cancer, it accounts for only a minority of cases (~5%) and is not the predominant site of malignant transformation. - **Option 4**: This describes the anterior fibromuscular stroma (marked **D**), which is non-glandular tissue and is not a site of adenocarcinoma origin. Adenocarcinoma arises from glandular epithelium, not fibromuscular stroma. **High-Yield:** Peripheral zone cancer (70%) is palpable on DRE; transitional zone BPH is not—this anatomical distinction explains why they can coexist without direct causation. [cite: Robbins 10e Ch 21; Harrison 21e Ch 87]
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