The mechanical protector paradox: a hypothesis linking transition zone enlargement, urethral angle, and carcinogenesis via intraprostatic reflux

Abstract

The relationship between benign prostatic hyperplasia (BPH) and prostate cancer (PCa) remains paradoxical: both share inflammatory pathways, yet larger prostates often harbor less aggressive disease. This paradox may be explained by the mechanical interaction between the transition zone (TZ) and the peripheral zone (PZ). We hypothesize that urethral morphology, particularly a more acute prostatic urethral angle (PUA), acts as a primary biomechanical risk factor. A sharper urethral bend increases local hydrodynamic pressure and reflux potential, promoting the pro-inflammatory stimuli in the PZ. Conversely, we propose that progressive TZ enlargement acts as a “mechanical protector” against this insult. By compressing the PZ, the enlarging TZ narrows its ducts and reduces the intraprostatic reflux driven by the PUA. This effect attenuates the inflammatory microenvironment that drives malignant transformation. Integrating these factors, we propose a mechanical–inflammatory model in which prostate volume and urethral geometry jointly regulate intraprostatic inflammation. Integrating these factors, we propose a mechanical–inflammatory model in which prostate volume and urethral geometry jointly regulate intraprostatic inflammation. This hypothesis provides a unifying explanation for the inverse association between prostate size and cancer aggressiveness and suggests new imaging and mechanistic pathways for future investigations.