A 68-year-old Indian man presents with lower urinary tract symptoms and elevated PSA. Prostate biopsy shows adenocarcinoma. What is the most common histologic type and site of origin of prostatic adenocarcinoma?

Explanation

## Prostate Cancer: Histology and Anatomic Origin **Key Point:** Acinar (conventional) adenocarcinoma is the most common histologic type of prostate cancer, and it arises predominantly from the **peripheral zone** of the prostate. ### Histologic Classification of Prostate Cancer | Histologic Type | Frequency | Origin | Behavior | |-----------------|-----------|--------|----------| | **Acinar adenocarcinoma** | ~95% | Peripheral zone | Moderate to aggressive | | **Mucinous adenocarcinoma** | 1–2% | Transitional zone | More aggressive | | **Small cell carcinoma** | <1% | Central zone | Highly aggressive, neuroendocrine | | **Squamous cell carcinoma** | <1% | Anterior stroma | Rare, aggressive | | **Ductal adenocarcinoma** | <1% | Peripheral zone | Highly aggressive | ### Anatomic Zones of the Prostate **High-Yield:** Understanding prostatic anatomy is critical for understanding cancer distribution: 1. **Peripheral Zone (70% of gland)** — Site of ~75–80% of prostate cancers - Clinically palpable on DRE - Acinar adenocarcinoma arises here - Associated with elevated PSA 2. **Transitional Zone (5% of gland)** — Site of ~10–15% of cancers - Surrounds the urethra - BPH arises here (not cancer) - Mucinous and atypical cancers less common 3. **Central Zone (25% of gland)** — Site of ~5–10% of cancers - Surrounds the ejaculatory ducts - Small cell and neuroendocrine tumors rare 4. **Anterior Fibromuscular Stroma** — Rarely involved ### Acinar Adenocarcinoma: Key Features **Clinical Pearl:** Acinar adenocarcinoma is graded using the **Gleason score** (2–10), which predicts prognosis and guides treatment. The Gleason score is the sum of the two most common glandular patterns (each graded 1–5). **Mnemonic:** **ACINAR** = **A**denocarcinoma **C**arcinoma **I**s **N**early **A**lways **R**aised (in the peripheral zone) ### Why Peripheral Zone? - Larger surface area exposed to carcinogens - Longer epithelial lifespan - Proximity to the urethral sphincter (easier detection on DRE) - Age-related epithelial changes **Warning:** Do not confuse the **transitional zone** (site of BPH) with the **peripheral zone** (site of most cancers). BPH and cancer are independent, arise from different zones, and have different risk factors. ### Clinical Implications - **DRE findings:** Peripheral zone cancers are palpable as hard nodules - **PSA elevation:** Acinar adenocarcinoma raises PSA proportionally to tumor burden - **Biopsy strategy:** Systematic 12-core biopsy samples the peripheral zone predominantly [cite:Robbins 10e Ch 20]