Prostate tumors downregulate microseminoprotein‐beta (MSMB) in the surrounding benign prostate epithelium and this response is associated with tumor aggressiveness

Background Microseminoprotein‐beta (MSMB) is a major secretory product from prostate epithelial cells. MSMB synthesis is decreased in prostate tumors in relation to tumor grade. MSMB levels are also reduced in the circulation and MSMB is therefore used as a serum biomarker for prostate cancer. We hypothesized that cancers induce a reduction in MSMB synthesis also in the benign parts of the prostate, and that the magnitude of this response is related to tumor aggressiveness. Reduced levels of MSMB in the circulation could therefore be a consequence of reduced MSMB expression not only in tumor tissue but also in the benign prostate tissue. Methods MSMB expression was analyzed in prostatectomy specimens from 36 patients using immunohistochemistry and qRT‐PCR. MSMB expression in the benign prostate tissue was analyzed in relation to Gleason score, tumor stage, and distance to the tumor. Furthermore, Dunning rat prostate tumors with different aggressiveness were implanted into the prostate of Copenhagen rats to study if this affected the MSMB expression in the tumor‐adjacent benign rat prostate tissue. Results In prostatectomy specimens, MSMB expression was reduced in prostate tumors but also in the tumor‐adjacent benign parts of the prostate. The reduction in tumor MSMB was related to tumor grade and stage, and the reduction in the benign parts of the prostate to tumor grade, stage, and distance to the tumor. Implantation of Dunning cancer cells into the rat prostate resulted in reduced MSMB protein levels in the tumor‐adjacent benign prostate tissue. Rapidly growing and metastatic MatLyLu tumors had a more pronounced effect than slow‐growing non‐metastatic G tumors. Conclusion Our data suggest that aggressive prostate tumors suppress MSMB synthesis in the benign prostate and that this could explain why serum levels of MSMB are decreased in prostate cancer patients. This study suggests that markers for aggressive cancer can be found among factors altered in parallel in prostate tumors and in the adjacent benign tissue.