## Anatomical Zones of the Prostate and Cancer Origin ### Zonal Anatomy and Cancer Distribution **Key Point:** The peripheral zone is the site of origin in approximately 70% of prostate cancers, making it the most common location. | Prostatic Zone | % of Gland Volume | % of Cancers | Clinical Features | | --- | --- | --- | --- | | Peripheral zone | 70% | 70% | Most common site; palpable on DRE; detected by PSA screening | | Transition zone | 5% | 20% | Associated with BPH; may be missed on DRE | | Central zone | 25% | 5% | Rare site of origin; surrounds ejaculatory ducts | | Anterior fibromuscular stroma | — | <1% | Acellular; not site of cancer origin | ### Why Peripheral Zone? **High-Yield:** The peripheral zone is: 1. **Largest zone** — comprises 70% of normal prostate volume 2. **Accessible to DRE** — cancers here are palpable as nodules or induration 3. **Detectable by PSA** — peripheral zone cancers typically elevate serum PSA 4. **Site of acinar epithelium** — where adenocarcinoma arises ### Clinical Implications **Clinical Pearl:** Transition zone cancers (20% of cases) are often diagnosed at a lower PSA level because they compress the urethra and cause obstructive symptoms earlier, prompting investigation. However, they remain less common than peripheral zone cancers. **Warning:** Central zone cancers are rare (5%) and may be missed on digital rectal examination because they are deep and not palpable. They are often detected incidentally on imaging or biopsy for elevated PSA. **Mnemonic:** **PTC** — **P**eripheral (70%), **T**ransition (20%), **C**entral (5%) — remember the distribution of prostate cancer by zone.
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