Int J Med Sci 2019; 16(1):115-124. doi:10.7150/ijms.28735 This issue

Research Paper

Robo 4 - the double-edged sword in prostate cancer: impact on cancer cell aggressiveness and tumor vasculature

Andreas Pircher1#, Georg Schäfer2#, Andrea Eigentler3, Renate Pichler2, Martin Puhr3, Eberhard Steiner3, Wolfgang Horninger3, Eberhard Gunsilius1, Helmut Klocker3, Isabel Heidegger3✉

1. Department of Hematology and Oncology, Internal Medicine V, Medical University Innsbruck, Austria
2. Department of Pathology, Medical University Innsbruck, Austria
3. Department of Urology, Medical University Innsbruck, Austria
# both are first authors

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Pircher A, Schäfer G, Eigentler A, Pichler R, Puhr M, Steiner E, Horninger W, Gunsilius E, Klocker H, Heidegger I. Robo 4 - the double-edged sword in prostate cancer: impact on cancer cell aggressiveness and tumor vasculature. Int J Med Sci 2019; 16(1):115-124. doi:10.7150/ijms.28735. Available from

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Background: The magic roundabout receptor 4 (Robo 4) is a tumor endothelial marker expressed in the vascular network of various tumor entities. However, the role of Robo 4 in prostate cancer (PCa), the second common cause of cancer death among men in -developed countries, has not been described yet. Thus, the present study investigates for the first time the impact of Robo 4 in PCa both in the clinical setting and in vitro.

Methods and Results: Immunohistochemical analyses of benign and malignant prostate tissue samples of 95 PCa patients, who underwent radical prostatectomy (RPE), revealed a significant elevated expression of Robo 4 as well as its ligand Slit 2 protein in cancerous tissue compared to benign. Moreover, increased Robo 4 expression was associated with higher Gleason score and pT stage. In advanced stage we observed a hypothesis-generating trend that high Robo 4 and Slit 2 expression is associated with delayed development of tumor recurrence compared to patients with low Robo 4 and Slit 2 expression, respectively.

In contrast to so far described exclusive expression of Robo 4 in the tumor vascular network, our analyses showed that in PCa Robo 4 is not only expressed in the tumor stroma but also in cancer epithelial cells. This finding was also confirmed in vitro as PC3 PCa cells express Robo 4 on mRNA as well as protein level. Overexpression of Robo 4 in PC3 as well as in Robo 4 negative DU145 and LNCaP PCa cells was associated with a significant decrease in cell-proliferation and cell-viability.

Conclusion: In summary we observed that Robo 4 plays a considerable role in PCa development as it is expressed in cancer epithelial cells as well as in the surrounding tumor stroma. Moreover, higher histological tumor grade was associated with increased Robo 4 expression; controversially patients with high Robo 4 tend to exert lower biochemical recurrence possibly reflecting a protective role of Robo 4.

Keywords: Prostate cancer, Robo 4, Slit 2, cancer aggressiveness, tumor recurrence