Bache et al. BMC Cancer 2010, 10:132 http://www.biomedcentral.com/1471-2407/10/132 Page 6 of 8 Figure 2 Serum and tumor OPN protein levels and overall survival of STS patients. Analysis of serum (left) and tumor (right) OPN protein levels and overall survival of STS patients using a univariate Cox’s proportional hazard regression model. In comparison to patients with a low serum or tumor OPN-level (dotted line), an elevated OPN-level (bold line) correlates with a 2.2- (p < 0.05) or 3.7-fold (p = 0.01) increased risk of tumor-related death for STS patients. between OPN protein expression and outcome of osteo- sarcoma patients [23]. In this regard, Luo et al. were able to show that different osteosarcoma cell lines had significantly lower OPN levels than mature osteoblasts [32]. This may indicate that OPN has no significance for osteosarcoma tumor growth. However, antisense oligo- deoxynucleotides against human OPN reduced the tumorigenicity of xenotransplanted osteosarcoma tumors in nude mice [33]. Additionally, our analysis shows that siRNA-induced osteopontin inhibition results in reduced clonogenic survival and migration of soft tis- sue sarcoma and breast cancer cell lines (Hahnel et al., manuscript submitted). Our analysis of tumor OPN mRNA expression of 68 soft tissue sarcoma patients did not show any associa- tion with clinical parameters or prognosis. In contrast, another study of 41 osteosarcoma patients did show that a high OPN mRNA level is correlative with overall sur- vival, event-free survival and relapse-free survival [34]. Moreover, a study of 15 adult soft tissue sarcoma patients showed a significant increase of OPN mRNA levels compared to normal tissue [22]. In addition, OPN splice variants may be involved in tumor progression. In particular, osteopontin-c has been postulated to be a significant factor for glioma [35], breast cancer [17,36] and hepatocellular carcinoma [37]. Clearly, more data are needed to characterize the role of osteopontin mRNA in sarcomas. Conclusion In the present study, we analyzed OPN mRNA and pro- tein levels in tumors and the OPN protein levels from the serum of 93 soft tissue sarcoma patients. Our data suggest that increased serum and tumor OPN protein levels are significantly associated with clinical para- meters, such as tumor stage, tumor grade, subtype of tumor, tumor size and the rate of relapse. In addition, using a univariate Cox’s proportional hazards regression model, we found that an elevated OPN protein level in the serum and tumor tissue extracts is a significant negative prognostic factor for patients with STS. Our data suggest OPN protein in serum as well as in tumor tissue extracts is an important prognostic factor for soft tissue sarcoma patients. Acknowledgements This work was supported by the Wilhelm Sander Stiftung (grant number: 2007.123.1). We thank our colleagues from the Department of Radiotherapy, the University of Halle, for their contribution and continuous support on this study. We thank Astrid Katzer from the University of Würzburg for her excellent technical assistance as well. Helge Taubert was supported by the Deutsche Krebshilfe (grant number: 107590). Author details 1Department of Radiotherapy, Martin-Luther-University Halle-Wittenberg, Halle, Germany. 2Department of Oral and Maxillofacial Plastic Surgery, Martin- Luther-University Halle-Wittenberg, Halle, Germany. 3Radiation Oncology, University of Würzburg, Würzburg, Germany. 4Institute of Pathology, Dresden University of Technology, Dresden, Germany. 5Department of Surgery, Malteser St Franziskus Hospital gGmbH, Flensburg, Germany.