Category Total Tumor stage I II III IV Tumor type LS FS+MFH NS RMS+LMS Other STS Tumor size T1 T2 Distant metastasis M0 M1 Relapse R0 R1 Follow-up Alive Dead Kaplan-Meier analysis mean survival in months Cox’s-Regression model RR CI 21 8 10 2 1 12 4 0 3 2 6 15 21 0 15 6 14 7 103 p = 0.004* p = 0.002* p = 0.03* p = 0.12 p = 0.41 p = 0.04* p < 0.05* 2.2 1.0-5.1 65 6 27 24 8 9 20 8 19 9 6 59 58 7 40 25 29 36 60 7 7 4 2 10 3 2 4 1 3 17 18 2 17 3 16 4 68 p = 0.06 p = 0.07 p = 0.85 p = 0.82 p = 0.02* p = 0.007* p = 0.01* 3.7 1.3-10.4 60 6 25 22 7 11 17 5 18 9 8 52 55 5 34 26 21 39 58 17 5 7 5 0 5 6 2 3 1 1 16 17 0 12 5 11 6 72 p = 0.21 p = 0.19 p = 0.24 p = 0.14 p = 0.88 p = 0.2 p = 0.21 1.7 0.7-4.3 51 7 19 17 8 13 11 1 17 9 9 42 45 6 35 16 23 28 65 Bache et al. BMC Cancer 2010, 10:132 http://www.biomedcentral.com/1471-2407/10/132 Page 5 of 8 Table 3 Association of serum and tumor OPN levels with clinical parameters in soft tissue sarcoma patients Serum OPN protein level in ng/ml ≤ 516.54 >516.54 Tumor OPN protein level in ng/mg ≤ 34.34 20 >34.34 Tumor OPN mRNA level in molecules/pg HPRT ≤ 0.576 >0.576 p* value was significant, when p < 0.05. Abbreviations: OPN: osteopontin, LS: liposarcoma, MFH: malignant fibrous histiocytoma; FS: fibrosarcoma; NS: neurogenic sarcoma; LMS: leiomyosarcoma; RMS: rhabdomyosarcoma; STS: soft tissue sarcoma; RR: relative risk of tumor-related death; CI: confidence interval of tumor- related death. results Nordsmark et al. (2007) detected no correlation between plasma OPN and tumor OPN protein levels in patients with head and neck cancer (p = 0.75). Further- more, own in vitro studies detected a clear decrease of extracellular OPN protein levels after transfection with OPN siRNA in MDA-MB231 cells. In contrast, the intracellular OPN protein level was only partially decreased (Hahnel et al., manuscript submitted). More studies on the functions of intracellular OPN forms are necessary to understand their relationship with extracel- lular OPN and their tumor biological role. Our data suggest that increased serum and tumor OPN protein levels are significantly associated with clin- ical parameters, such as tumor stage, tumor grade, sub- type of tumor, tumor size and the rate of relapse (Table 3). In the Kaplan-Meier analysis, a significantly decreased overall survival was observed for patients with strong OPN protein expression in their serum (p = 0.04; Table 3) and tumor tissue (p = 0.007; Table 3). Further- more, the univariate Cox’s regression hazard model demonstrated that STS patients with a high serum and tumor OPN protein level have an increased risk of tumor-related death of 2.2 (p < 0.05) and 3.7 (p = 0.01; Fig. 2), respectively (Table 3). This is in agreement with a previously reported immunohistochemical study of 33 soft tissue sarcoma patients that showed an increased OPN level significantly correlated with higher tumor stage, grade and overall survival [22]. Furthermore, pri- mary sarcomas of the pulmonary artery display an abun- dant immunohistochemical OPN protein staining of tumor cells and extracellular matrix. Therefore, OPN protein may play a substantial role in tumor progression of vessel sarcomas [21]. However, an immunohisto- chemical OPN study did not find any correlation