Prostate cancer is one of the most common age-related malignancies. The occurrence frequency of prostate cancer is very different according to prostate zones. The prostate stroma is an important element in growth and differentiation of the normal prostate and also has a close relationship to the occurrence of benign prostatic hypertrophy and cancer. We examined 14 cases of normal prostate tissues obtained at autopsy and 11 cases of prostate cancer tissues at radical prostatectomy specimens with cancers for clarifying the characteristics of stromal components in the normal prostate and the correlation between the stroma and the occurrence of prostate cancers. Stromal cells, such as smooth muscle cells, myofibroblasts and fibroblasts were identified by immunohistochemistry (IHC). Connective tissue fibers were detected by Elastica van Gieson and also IHC stain. Quantitative analysis of the smooth muscle tissue and connective tissue fibers were performed using a computer image analyzer system. In the normal prostate, stromal components varied in each zone. Every zone of the prostate contained smooth muscle cells, myofibroblasts, fibroblasts and collagen fibers. Elastic fibers were clearly visible in the transition zone. Smooth muscle cells were the main stromal component but less numerous in the frequent occurrence zone (peripheral zone) of prostate cancer (p<0.05). Myofibroblasts and fibroblasts were found either in normal or cancer tissues, although a few in number. The increase of collagen fibers accompanied decrease of smooth muscle cells as prostate cancer grade increased (p<0.05). The characteristics of stromal components and their amounts in the normal prostate appear to correlate with a distinct predilection for cancer occurrence in the peripheral zone and a weak stromal reaction in prostate cancers.

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